Circuit Diagram

AC to DC Voltage Converter Circuit

Published:2013/10/17 20:24:00 Author:lynne | Keyword: AC to DC Voltage Converter Circuit

This AC to DC converter circuit is capable of converting an alternative voltage within 70V – 260V range into a DC voltage within 180V to 350V DC range, so it can be used for 110V and 220V too. To achieve this voltage conversion we use a MC34161 rectifier as a voltage doubler at low input voltages and as a classic rectifier at high input voltages. MC34161 includes a reference power supply which delivers 2.54V at pin 1. The signal level applied at pin 2 is internally compared with a 1.27V voltage.D5 zener diode, togheter with R1 and C4 provide IC’s required 12V voltage. Capacitor’s voltage of C2 and C3 must be greater than 250V.   (View)

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Increase Regulator Voltage Output

Published:2013/10/17 20:22:00 Author:lynne | Keyword: Increase Regulator Voltage Output

It is often necessary to arrange an voltage regulator IC to give a higher output voltage than that set by the regulator alone. One method to achieve this is by connecting the “common” terminal to the mid-point of a potential divider but the problem with this method is that IC regulators have a small quiescent current (~10mA) flowing out of the common terminal to ground.The magnitude of this quiescent current is not closely controlled and hence the total output voltage becomes somewhat unpredictable. Low divider resistor values help, but there are likely to be complications of heat dissipation and inefficiency. The circuit presented here avoids the problem by using the transistor T1 to generate a low impedance at the regulator common terminal by emitter-follow action, while transferring the voltage divider from a relatively high-resistance divider network. The value of R3 is not critical but must be low enough to accept the highest quiescent current without causing T1 to turn-off.   (View)

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Relay Driver Circuit 2

Published:2013/10/16 20:20:00 Author:lynne | Keyword: Relay Driver Circuit 2

Relays have been around for a long time and though often now replaced with solid state switches, they have unique properties that make them more robust than solid-state devices and are not going away. The unique properties are high current capacity, ability to withstand ESD and drive circuit isolation. There are numerous ways to drive relays. In preparation for some of the more advanced relay drivers I will be posting in the future, I have listed a few basic relay drivers for your reference. Included are the following: High side toggle switch driver, low side toggle switch driver, bipolar NPN transistor driver, Darlington transistor driver, N-Channel MOSFET driver, and ULN2003 driver. Relay Driver Schematic Advantages of the low side driver Easy to interface to low voltage logic circuitry Far more interface options including the popular ULN2003 driver Fewer components Uses more commonly available and less expensive NPN drive transistors Relay power may be sourced by a higher, unregulated voltage—reduces load on voltage regulator Easier to interface relay economy feature—will be discussing this in the future Industry standard technique Relay driver, how it works? Generally, we think on the high side because we usually place the power switch in the power lead as in Fig 1. The same may be accomplished by locating the switch in the low side or return lead as in Fig 2. When controlling relays via logic etc. it is far easier to interface to the low-side driver. For low power relays, a 2N4401 is a good choice (Fig 3). If you desire to drive a larger relay or want less base current, a Darlington driver (Fig 4) is recommended. If driving via CMOS logic, an enhancement mode MOSFET is a good choice (Fig 5). If you nave a number of relays or other loads to drive (like a 7 segment LED display), the ULN2003 is a great choice. (Fig 6). Clamp diode The clamp, free-wheeling or commutation diode provides a path for the inductive discharge current to flow when the driver switch is opened. If not provided, it will generate an arc in the switch—while the arc will not generally damage a switch contact, it will cause contact degradation over time—and yes, it will destroy transistors—been there, done that. The diode requirements are non-critical and a 1N4148 signal diode will generally work OK in low power applications. The ULN2003 has internal clamp diodes. While these work OK in non-critical applications, I have had problems with them generating “glitches” in supposedly unrelated sections. Avoid emitter follower drivers I have not included an example of this because I do not wish to promote this technique. This is a high-side driver accomplished by an emitter follower transistor. They are frequently found on electroschematics.com, but they are not the driver of choice for three reasons as follows: It turns the relay itself into a voltage threshold detection device—while it may work, it was not designed for this function and the threshold may vary greatly from device to device. The emitter follower transistor requires a base drive voltage that should go essentially to the positive rail or the relay may not pick up. Only relays that have a low pick-up voltage work OK. The voltage hysteresis is extreme—once turned on, it is often difficult to turn off again. For the future Relay economy driver circuits Voltage doubler relay driver Glossary of undocumented words and idioms (for our ESL friends) glitch –undesirable noise transient or spike (in electronics)   (View)

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Adjustable Voltage Regulator with TDA2030

Published:2013/10/16 20:16:00 Author:lynne | Keyword: Adjustable Voltage Regulator with TDA2030

This Adjustable Voltage Regulator is made by combining a common 78L05 with an integrated audio amplifier of the type TDA2030, an adjustable voltage regulator can be constructed in a very simple manner that works very well. The output voltage is adjustable up to 20 V, with a maximum current of 3 A. Since the TDA2030 comes complete with a good thermal and short-circuit protection circuit, this adjustable regulator is also very robust. As illustrated by the schematic, the design of this circuit is characterized by simplicity that is hard to beat. In addition to the two ICs, the regulator contains actually only two potentiometers and a few capacitors. The adjustment is done by first turning potentiometer P1 to maximum (wiper to the side of the 78L05) and subsequently turning trimpot P2 until the desired maximum output voltage is reached. P1 is then used to provide a continuously adjustable voltage between this maximum and nearly zero volts. At relatively small output currents there are no specific requirements regarding the cooling. However, when the output current exceeds 1 A, or if the input to output voltage difference is quite large, the amplifier IC has to dissipate too much power and a small heatsink is certainly appropriate. Variable Voltage Regulator Circuit Diagram   (View)

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TDA7294 Datasheet

Published:2013/10/16 20:13:00 Author:lynne | Keyword: TDA7294 Datasheet

The TDA7294 is a monolithic integrated circuit in Multiwatt15 package, intended for use as audio class AB amplifier in Hi-Fi field applications (Home Stereo, self powered loudspeakers, Topclass TV). Thanks to the wide voltage range and to the high out current capability it is able to supply the highest power into both 4Ω and 8Ω loads even in presence of poor supply regulation, with high Supply Voltage Rejection. The built in muting function with turn on delay simplifies the remote operation avoiding switching on-off noises. TDA7294 Features DMOS power stage very high operating voltage range high output power (up to 100W music power) muting/stand-by functions no switch on/off noise no boucherot cells very low distortion very low noise short circuit protection thermal shutdown   (View)

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LM3886 Datasheet

Published:2013/10/15 20:36:00 Author:lynne | Keyword: LM3886 Datasheet

The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4Ω load and 38W into 8Ω with 0.1% THD+N from 20Hz–20kHz. The performance of the LM3886, utilizing its Self Peak Instantaneous Temperature ( SPiKe™) protection circuitry, puts it in a class above discrete and hybrid amplifiers by providing an inherently, dynamically protected Safe Operating Area (SOA). SPiKe protection means that these parts are completely safeguarded at the output against overvoltage, undervoltage, overloads, including shorts to the supplies, thermal runaway, and instantaneous temperature peaks. LM3886 Applications component stereo compact stereo self-powered speakers surround-sound amplifiers high-end stereo TVs   (View)

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TDA2822 Datasheet

Published:2013/10/15 20:29:00 Author:lynne | Keyword: TDA2822 Datasheet

The TDA2822 is a monolithic integrated circuit in 12+2+2 powerdip, intended for use as dual audio power amplifier in portable radios and TV sets.TDA2822 features supply voltage down to 3V low crossover distorsion low quiescent current bridge or stereo configuration   (View)

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12V DC to 120V AC Inverter Circuit

Published:2013/10/15 20:21:00 Author:lynne | Keyword: 12V DC to 120V AC Inverter Circuit

Here is a simple 12 volts DC to AC inverter circuit. This 120V AC power source is built with a simple 120V:24V or 110V:24V center-tapped control transformer and four additional component. This circuit outputs a clean 200-V pk-pk square wave at 60 Hz and can supply up to 20W. The circuit is self-starting and free-running.If Q1 is faster and has a higher gain than Q2 is will turn on first when you apply the input power and will hold Q2 off. Load current and transformer magnetizing current then flows in the upper half of the primary winding, and auto transformer action supplies the base drive until the transformer saturates.When that action occurs, Q1 loses its base drive. As it turns off, the transformer voltage reverse, turning Q2 on and repeating the cycle. The output frequency depends on the transformer iron and input voltage but not on the load. The frequency range between 50 to 60 Hz with a 60-Hz transformer and car battery or equivalent source. The output voltage depends on turns ratio and the difference between input voltage and transistor saturation voltage. For higher power, use larger transformers and transistors. This type of 12V inverter normally is used in radios, phonographs, hand tools, shavers and small fluorescent lamps. It will not work with reactive loads (motors) or loads with inrush currents, such as coffee pots, frying pans and heaters.   (View)

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HV4205E Single Chip Voltage Converter

Published:2013/10/14 20:04:00 Author:lynne | Keyword: HV4205E Single Chip Voltage Converter

With HV4205E you can build a simple single chip voltage converter. With IC and a few external components connected like in the schematic you can obtain dc stabilized voltages between 5 to 24V directly from main power source (100 to 260V ac). The maximum output current is 50mA.The main chip contains a preregulator which ensure C2 charging voltage (a large capacitance). The charging process continues untill the capacitor voltage has reached a level of approximately the desired voltage + 6V.When this stage is reached, C2 delivers the required voltage to the regulator, the output of this regulator can be adjusted between 5V and 24V with P1 and is available at IC pin 6. Voltage converter schematic   (View)

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Wide Frequency Range 555 VCO

Published:2013/10/14 20:02:00 Author:lynne | Keyword: Wide Frequency Range 555 VCO

The 555 frequency can be varied via adjusting the voltage at pin 5. However, the range and linearity of frequency adjustment is very limited. This is a way to greatly improve performance using the inverted 555 timer circuit that was previously posted. 555 VCO Schematic Current source Q2 is connected in the common base configuration. In this mode of operation, the collector current is a function of emitter current regardless of the collector voltage. In this way, it can perform a linear charge function upon C1. The emitter must be driven from a negative supply voltage. Frequency is scaled to 10V = 10kHZ via R5. Frequency range in this set-up is 180 to 10kHZ. Bias transistor Q3 is wired as a self-biasing transistor by connecting the base to the collector and feeding it a bias current via R4. Voltage drop is 0.6V. Originally, I had a 1N4148 diode and its voltage drop was 0.45V that added too much offset to the emitter of Q1. Ideally, the voltage drop across Q3 should equal Vbe of Q2. This is a compromise because they are matched only under the condition of Ie = (9V – 0.6V) /R4 = 84uA. The emitter current varies from about 3 to 303uA. Lowest low end offset would occur with both transistors matched and R4 increased to 3M—in that case, the hFE @ 3uA must >100—this looks practical, but would require a different transistor selection—I did not experiment with this option.   (View)

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Greenhouse Heater Temperature Control

Published:2013/10/14 19:59:00 Author:lynne | Keyword: Greenhouse Heater Temperature Control

Standard resistance heaters used for space heaters sometimes have thermostats, but these are not adjustable to the low temperature settings required for winter greens. Instead of purchasing a high end programmable temperature controller, I fabricated this greenhouse heater temperature control project circuit. It cycles an electric heater. It has been operating for two winters now with good results, and I just added the LEDs so I could tell from a distance if it was functioning. Temperature Control Circuit Schematic Key components are documented on the schematic – there is no bill of materials. Power supply Basic transformer isolated full-wave center-tapped configuration with LM7812 voltage regulator Temperature probe This is simply (4) 1N4148 diodes connected in series with a thermal anticipation resistor (R1) heat shrunk together at the end of a (3) wire signal cable—it is visible on some of the photos. The use of a thermal anticipation resistor is an old HVAC thermostat technique that adds negative feedback to the system by immediately heating the temperature sensing device slightly. It forces short cycles and prevents temperature overshoot. Because the amount of power to apply to the thermal anticipation resistor was unknown, I incorporated a power level pot (R6). I later determined that it works quite well at the maximum setting, so the pot is not required. Although the temperature measurement can be accomplished via a single diode, four diodes in series are used to get the signal “out of the mud.” The inexpensive LM324 op amp has a maximum input offset voltage of 7mV, so the higher level voltage signal helps to improve performance. The diodes are biased at approx 4mA via R2. Comparator U1C is connected as a voltage comparator with positive feedback via R5. Positive feedback prevents relay chatter. C3 is an input noise filter capacitor. As the temperature cools, the voltage drop across the probe diodes increases. When it reaches the set point, the output changes states and the positive feedback through R5 further increases the non-inverting input by 5mV to assure that it remains latched until the temperature increases and the voltage drops below the set point. Calibration In a previous circuit http://www.electroschematics.com/409/diode-electronic-thermometer/ we see that the temperature coefficient of silicon diodes is approx. -2mV /°C. (4) in series boosts it to -8mV /°C. I dropped the probe in ice water and measured the voltage—2.773V in my case. Then I calculated what the voltage would be at 4.4°C (40°F). Then I adjusted the voltage at the calibration pot R8 to get 2.738V—this is the set point. Proper operation was subsequently determined by placing the probe in and out of ice water to observe cycling of the relay. Relay driver Q1 is a simple NPN relay driver. For more information check out this post: http://www.electroschematics.com/7123/relay-driver-2/Quencharc RC-1 is connected across the relay contacts to reduce arcing. These are unreasonably expensive, so I recommend using a discrete resistor and capacitor. Polypropylene is the capacitor of choice—just make sure that it has sufficient AC voltage rating; LED Driver U1A is another comparator that drives the LEDs. Red indicates power ON and Green indicates OFF. Greenhouse specifications For a guide for estimating your power requirements, compare your greenhouse with the following: Dimensions: 8ft wide x 12ft long x 7ft high. North side is insulated by high density foam to minimize heat loss East and West ends have a double layer of plastic sheeting South side and top are single layer greenhouse plastic—UV resistant—long life Latitude is 40oN.   (View)

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Quirky 555 Timer Reset Function

Published:2013/10/13 20:39:00 Author:lynne | Keyword: Quirky 555 Timer Reset Function

How many have had legitimate problems with the 555 timer? Let me guess…it involved the reset line, did it not? We all know that pin 4 must be set high before oscillation begins, but what is its threshold? input current? and what happens when it is operated slightly out of spec? This may be the very first attempt in documentation of this obscure phenomenon. 555 pin 4 reset behavior schematic Method To determine reset threshold, a transistor integrator generates a low impedance, negative-going ramp voltage signal that integrates from +5V to –0.65V. To obtain the negative voltage, the power supply is split to provide –0.7V. While it is slowly changing at the rate of -1V /S (trace 1), pins 2 & 6 are monitored for oscillation (trace 2). A 3rd trace monitors the output (pin 3). All data is logged on the spreadsheet. A total of (8) devices were tested, including (2) CMOS TLC555N devices.When running, the 555 oscillates at approx. 100hZ. Vcc = 5V.   (View)

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LDR Pole Light Switch

Published:2013/10/13 20:38:00 Author:lynne | Keyword: LDR Pole Light Switch

My vintage (62 year old) pole light has always been controlled by a timer—a source of continual frustration due the requirement of readjustment for the ever-changing seasons. However, after knocking it over (I backed my car into it…), I decided it was time for an update. The circuit consists of a light dependent resistor (LDR), TLC555 (applied as Schmitt trigger), and a TRIAC power switch. The complete assembly neatly fits inside the steel pole light tube and the LDR peeks out through a hole in the side. This was really a fun project, and useful to boot. Pole Light Switch Circuit Schematic Power supply The power supply is the typical capacitor limited charge pump type that is zener regulated at 6.2V. Due to the lack of isolation, I was careful to identify the return conductor so that the electronics (including the LDR) would not be floating on the hot lead. For safety, most of the testing was done using an isolation transformer. R1 must absorb a high peak power transient current when power is applied, so a carbon comp, ceramic comp, or wire wound resistor is recommended. Maximum DC current available is 16mA. Actual load is about 6mA. My application was 115V, 60hZ. For 230VAC, the components are indicated on the schematic. In this circuit, +6V is the power return lead, and 0V is the electronic circuit common—to visualize this, one must screw his head on backwards… LDR The light dependent resistor (CdS photocell) that I used was in the TO-5 package that is well adapted for poking through a hole and is held in place with silicone rubber. The Clairex CL703M19 LDR that I used is no longer available and I have been unable to locate the specs. The DigiKey PDV-P8103-ND appears to be a reasonable choice, but may require bias current tweaking to set the threshold. 555 Schmitt trigger driver A TLC 555 was used as a voltage threshold detecting device with hysteresis. Pin 7 drives the TRIAC gate directly via its open collector output. This is a rather unconventional application. The CMOS version is used to minimize power supply load—I tried a bipolar 555 and it worked, but the power supply ripple voltage doubled to about 0.5VP-P. Constant current bias—Threshold adjustment Because the 555 has so much hysteresis, I feared that the ON & OFF thresholds would be too far apart. To help reduce the hysteresis, the LDR is biased by a current source. Q1 is wired as a current source—its collector current does not vary with collector voltage. This technique essentially increases the “gain” of the LDR. The current is set via adjusting the emitter resistor (R3)—it drops about 0.37V. C3 makes the circuit insensitive to rapid changes in light intensity. It takes about 60sec to turn on. Logic TRIAC The logic TRIAC is an interesting device. It can be triggered by either a positive or negative gate current regardless of voltage blocking polarity. For maximum sensitivity, I used negative gate current. The device I used had an actual Igt (gate current sensitivity) of 1.5mA that is well below the 5mA Max specification. However, gate overdrive (5mA in my case) is recommended to assure that it fires at low winter temperatures. Quencharc RC-1 is connected across the TRIAC to help control turn-off voltage transients. Choice of lighting For the time being, I am sticking with the vintage incandescent lamp—it is a matter of aesthetics. I will upgrade to LED technology only when its color balance matches incandescent.   (View)

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Single Pushbutton Run-Stop Circuit

Published:2013/10/13 20:37:00 Author:lynne | Keyword: Single Pushbutton Run-Stop Circuit

There are solutions to this problem—mechanical (push On/push Off switch), electromagnetic (latching relay) and electronic (CMOS logic), but few (if any) good discrete electronic solutions. I have scoured the web, looking for such and have not found any decent circuits. One recent job required such and I had to resort to CMOS logic — I will be posting that one in the future. As a result, I have been racking my brain for the last few months and have finally come up with a really neat circuit. It is a little busy, having 19 components, but they are small, inexpensive and commonly available. What are the benefits of such a circuit? Good question — one may wonder what use this could be. Besides being compatible with any normally open pushbutton, it is a great way to add multiple pushbuttons to a system—all normally open pushbuttons are simply wired in parallel — any can start or stop the device. Also note that push-on/push-off switches are quite special and have a limited offering in regard to size, mechanics and aesthetics—they also have an unpleasant feel, in my estimation. Single Pushbutton Run-Stop Schematic How it works When the pushbutton is initially closed, it directly turns on the gate of Q1 via D2. Q1 turns on after a brief delay determined by the charge time of C1. Q1 then biases Q2 on, and Q2 seals in the pushbutton signal and C2 charges up to 12V via R8 and D2. When the pushbutton is closed again, the top side of C2 is grounded via the pushbutton action through D1. The lower side of C2 goes negative and dumps half of its charge into C3. The negative voltage on C3 turns on Q3 that is connected in the common collector configuration (emitter follower). The emitter of Q3 shorts the bias voltage of Q2 to common thus turning off Q1 (as soon as the pushbutton is released).   (View)

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555 Door Ajar Flasher

Published:2013/10/11 20:52:00 Author:lynne | Keyword: 555 Door Ajar Flasher

How it works The flasher is the standard 555 oscillator circuit that drives an ultrabright white LED for daylight visibility. Repetition rate is about 2hZ and the duty cycle is about 10%. Peak LED current is 60mA, but average is 6mA. Since the door is supposed to remain closed most of the time, the circuit power is controlled by a 2N7000 N Channel MOSFET. When the reed switch is closed (sensing the magnet), it shorts out the gate drive signal to the transistor and turns off the oscillator. At this time the battery drain is only 9uA. Note that there seems to be no convenient way to turn off the 555 in such a way that it does not draw much current. Grounding pin 4 stops oscillation, but turns on the LED continuously. C2 provides voltage transient protection for the MOSFET gate. LED brightness is controlled by R5—YIKES! do not look into the LED like I did… The reed switch This circuit uses the commonly available NC (normally closed) reed switch. A NO variety would be easier to use, but such is rare and expensive. If the circuit is packaged inside a small plastic enclosure, the reed switch could be cemented into one edge of the box thus protecting the glass tube from damage. The reed switch I used for the test is packaged in a plastic tube. It is quite sensitive — can sense the magnet at 2 to 3cm.   (View)

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Single Transistor Amplifier Revisited – Part 1

Published:2013/10/11 20:51:00 Author:lynne | Keyword: Single Transistor Amplifier Revisited – Part 1

Circuit and Biasing Technique There is so much to learn about the single-transistor amplifier, that this brief tutorial hardly scratches the surface. This discussion considers only the common-emitter configuration as applied to low level audio. History In the early days of solid state amplifiers, thermal stability was the big issue. The first devices available were leaky germanium PNP transistors. The collector to base leakage was often so excessive that it could cause thermal run-away because the leakage increased exponentially with temperature. The classic way of keeping this under control was the base divider-emitter swamping resistor topology. Early text books (including the one I used in 1963) had a detailed section on this and included a mathematical calculation for “stability factor.” Unfortunately, now (some 50 years later), we are still suffering from vestiges of this approach as we continue to see the same circuits popping up even though germanium transistors have been obsolete and unavailable for well over 30years, and the silicon bipolar NPN has been long the transistor of choice. Since leakage in silicon devices is so low that it can hardly be measured, we can make a fresh start. Self-Biased Circuit Schematic A stable quiescent operating point (“Q” point) can be established simply by sourcing the base divider from the collector voltage. This dispenses with the emitter swamping resistor. While not perfect, it provides predictable results and simplicity. It is good for low power amplifier transistors that dissipate less than about 100mW. R1, 2 & 3 form the base divider. The juncture of R2 & 3 is bypassed to common via C2 to eliminate negative feedback from the collector—this negative feedback tends to reduce voltage gain. We will be covering negative feedback in the future. C1 is the input coupling capacitor and C3 is the output coupling capacitor—both pass the AC signal while blocking the DC component. To accommodate a wide range of hFE’s, the base divider current is in the range of 5 to 10 * base current. Operating point calculations (ohms law) Set collector voltage: My rule-of-thumb is to set it at about 40% of Vcc. In this case it is 5V. Calculate collector current: Ic = (Vcc – Vc) /R4 = (12V – 5V) /2.2K = 3.2mA. Calculate base current: Ib = Ic / hFE = 3.2mA /200 = 16uA (using the common 2N3904) Establish base divider current: Id = Ib * 5 = 16uA * 5 = 80uA (a factor of 5 is good) Calculate Ir1: Ir1 = Id – Ib = 80uA – 16uA = 64uA Calculate R1: R1 = Vbe / Ir1 = 0.65V /64uA = 10K Calculate R2 + R3: R23 = (Vc – Vbe) /Id = (5 – 0.65V) /80uA = 54K Calculate R2,3: R2 = R3 = 54K / 2 = 27K (may be unequal, but total must be 54K)   (View)

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555 Christmas Lights

Published:2013/10/11 20:50:00 Author:lynne | Keyword: 555 Christmas Lights

Though a Christian by personal faith in Jesus Christ, I am not big on Christmas decorations except for the traditional Christmas tree. However, this 555 flasher project is an exception. This is a take-off on the previous Firefly Lights Circuit posting. I had a strip of four tiny PCB’s remaining, so I built them up before separating them — and never did separate after observing operation. The result is nothing short of amazing. Instead of boring repetitive (predictable) flashing, they are in no way synchronous. This makes for a captivating watch — something like watching a fire… Hang this on your Christmas tree as an ornament.   (View)

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Relay Economy Circuit

Published:2013/10/10 20:12:00 Author:lynne | Keyword: Relay Economy Circuit

Relays continue to be useful and popular, but in low-power, battery operated applications they tend to be power wasters. The following relay economy circuits reduce coil power significantly by simply adding a series resistor. As soon as the relay picks up, the coil voltage is reduced either by the normally closed contact opening or the charging of a capacitor that is connected in parallel with the economy resistor. Included is the standard relay economy circuit as well as two additional circuits that may be new to the world. Note that these relay economy circuits may be used in conjunction with the relay driver circuits previously posted: www.electroschematics.com/7123/relay-driver-2/ Figures 1 & 2 show how high and low side drivers can be connected to provide relay economy. The unused normally open relay contact provides the output. If an isolated contact is required, a two pole relay must be used as in figure 3. Figures 4 & 5 solve the problem by simply adding a capacitor in parallel with the resistor. This allows the use of a single pole relay. The required capacitance is high, but voltage is low so that the size is physically manageable. Figure 6 shows how to reduce the capacitor size by a factor of 20 by use of a simple transistor integrator. The collector voltage of Q1 integrates to the maximum voltage allowed by R1 in about 25mS. Red arrows indicate capacitor charge pathGreen arrows indicate capacitor discharge pathC1 integrates slowly due to the limited current flowing through R2. The voltage across R2 is limited by the Vbe of Q1 (0.7V) while integrating.   (View)

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Bicycle Anti-Theft Alarm Circuit

Published:2013/10/10 20:09:00 Author:lynne | Keyword: Bicycle Anti-Theft Alarm Circuitv

I hate to suggest the specific application ‘bicycle’ because it may be use to protect many items from theft. This anti-theft alarm project is built around the inexpensive Measurement Specialties DT piezo film sensor. Every now and then everything seems to work out perfectly as in the Yin and Yang of the cosmos, and this is one of them.It is simple, inexpensive and practical…   (View)

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MAX232 Circuit

Published:2013/10/10 20:06:00 Author:lynne | Keyword: MAX232 Circuit

The MAX232 datasheet specifies that the IC is a dual driver/receiver that includes a capacitive voltage generator to supply TIA/EIA-232-F voltage levels from a single 5-V supply. Each receiver converts TIA/EIA-232-F inputs to 5-V TTL/CMOS levels. These receivers have a typical threshold of 1.3 V, a typical hysteresis of 0.5 V, and can accept ±30-V inputs. Each driver converts TTL/CMOS input levels into TIA/EIA-232-F levels. MAX232 Applications/Uses Battery-Powered RS-232 Systems Interface Translation Low-Power Modems Multidrop RS-232 Networks Portable Computing MAX232 Features Meets or Exceeds TIA/EIA-232-F and ITU Recommendation V.28
Operates From a Single 5-V Power Supply With 1.0-
F Charge-Pump Capacitors
Operates Up To 120 kbit/s
Two Drivers and Two Receivers
±30-V Input Levels
Low Supply Current… 8 mA Typical
ESD Protection Exceeds JESD 22 − 2000-V Human-Body Model (A114-A) Upgrade With Improved ESD (15-kV HBM) and 0.1-
F Charge-Pump Capacitors is Available With the MAX202   (View)

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