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  1. M

    Generating 24VAC Output (2 Amp Capability) from 36-40VDC

    Hello, I am wanting to generate a 24VAC output, and be able to put up to a 2 amp load on it. The available power is 36VDC or 40VDC (3 or 4 amp). No transformer - this has to be generated off the main DC voltage. As we know, a 24VAC output consists of a sinewave with a peak voltage of +34VDC and...
  2. M

    Capacitance Measuring Circuit - Can This Circuit Be Changed For Higher Frequency?

    I came across this circuit that measures capacitance mainly between 30pF and 300pF, and is typically used between 31KHz and 250KHz. It basically outputs a 0-5V analog value that correlates with the capacitance. I drew a green arrow pointing to where the measurement is taking place. Its basically...
  3. M

    3 Phase Motor - 3 Individual Circuit Breakers - Detect if 1 Breaker Tripped And Shut Down Motor

    Hey guys, I am turning on and off a 3 phase motor using a triple pole relay. I am also using 3 individual circuit breakers (one for each phase). For this application, I can only use 3 individual circuit breakers/fuses, as opposed to a single circuit breaker that has 3 poles in it. I am wanting...
  4. M

    Resistor Pull-Up/Down Problems With Relay Driving Circuit And Darlington Transistor

    Hello, I created a relay driving circuit using an IO extender (PCF8574) and darlington transistors (MMBTA13). I was originally not aware that the IO extender can only source 100uA of current for an output... knowing that now I would probably design this quite differently. This is why I am...
  5. M

    Most inexpensive method for detecting if some current is flowing in 120VAC or 240VAC PCB Trace

    Hello, I am trying to figure out what is the most inexpensive method for detecting if current is flowing in a 120VAC or 240VAC PCB trace. I came across the ACS730, however this gives me the exact current that is flowing, and they are expensive. A simple yes or no would be preferable and I would...
  6. M

    Proper procedure for reducing ripple on DC power rail? (e.g. oscilloscope reading -> filter design)

    Hey guys, I have a 3.3 volt DC power rail. I have an integrated circuit that can only operate correctly if its power input has less than 30mV ripple. What is the procedure for building the corresponding filter circuitry to accommodate those requirements? Is there a reading I can take with the...
  7. M

    nRF24L01+ PA LNA - Seems that the PA (power amplification) portion of the module is failing?

    Hey guys, I have designed several circuits all of which use a nRF24L01+ PA LNA module (picture of it below). Occasionally we would come across a problem where the module will only transmit when you touch the module or antenna with your finger. This generally means that the transmission is...
  8. M

    Troubleshooting MH-Z14 CO2 Sensor Output Connected To Microcontroller - Sometimes readings go crazy

    Hey guys, I have some MH-Z14 CO2 sensors connected up to a Particle Photon microcontroller. Its a relatively simple circuit consisting of a 12vdc wall wort as power input, a 5v voltage regulator (RECOM R-78E5.0-1.0), a couple sensors, and a 12VDC fan. I have a bunch of these devices running in...
  9. M

    DS18B20 Temp Sensor - Working Intermittently & Not Reliable - Took Scope Readings & Could Use Advice

    Hey guys, I am using a Particle Photon (microcontroller w/ cloud connectivity) to communicate with a DS18B20 temperature sensor via the 1-wire bus. Below is how I have it wired up: From the research I have done, it seems to be preferred that you use 5 volts to power the sensor, then a pullup...
  10. M

    Built circuit w/ timer IC connected to SHDN pin of a voltage regulator - not shutting down properly?

    Hey guys, I built a circuit using a timer IC (TPL5111) connected up to the SHDN pin of a voltage regulator (MAX1724). Here is a simplified schematic of the intended use of the timer IC: The basic idea is that the device powers up, a microcontroller can do a few things, the microcontroller can...
  11. M

    Hot Swapping Headphone Jack - Temporary Shorts During Insertion - How To Remedy?

    Hey guys, I have a 3-wire temperature sensor (DS18B20) wired up to a headphone jack. I have the corresponding receptacle on the PCB. If the device is powered off before insertion of the plug, everything is fine. However, inserting the jack while the device is running causes the device to reset...
  12. M

    Power supply circuit question - Transformerless good idea? Still pass certification?

    Hey guys, I am in the process of deciding on a good rout to take for the power supply for my project. I had a couple of questions about it. More info on the device: The device is for home brewing, its a standalone device that sits on the floor, shelf, mounted to a frame, etc. Its actually...
  13. M

    Need help on converting 0-5v signal to 0-10v signal

    Hi guys, I am currently using a parallax propeller micro controller to generate a signal. I am using a ADC to create a 0-5v signal, and an op-amp to convert this into a 0-10v signal. I am experiencing a problem with it. Everything works fine until I go below 1.9v on the input of the op amp... at...
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