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  1. hevans1944

    More efficient LDR "dark" switch?

    Those three voltage measurements add up to exactly 3.563 V. Isn't that the battery terminal voltage you measured? Or am I missing something here? The internal resistance of the battery appears to be limiting the current through the LED. The LED forward voltage is high at 2.798 V because it isn't...
  2. hevans1944

    Recycling an old phone/fax machine any ideas?

    @JeanGenie who posted this thread is looking for some green PCBs circa 1970s era. It looks like your boards qualify. Maybe the two of you could work out some sort of a deal for you to ship one or two of those boards to Australia, with or without parts attached.
  3. hevans1944

    Magnet Alarm Circuit Board, Battery Power

    So, if you wire it back the way it was, including the piezo sound transducer, without the blue LED or the other batteries... just the three button cells,,, does it still work? Or have your managed to brick it with your battery adventures?
  4. hevans1944

    More efficient LDR "dark" switch?

    All good questions! You need to gather some more data. What is the voltage at the terminals of the battery when the LED is lit? What is the voltage across the 100 Ω resistor, the LED, and from the collector to emitter of the transistor? The last three measurements should add up to the battery...
  5. hevans1944

    More efficient LDR "dark" switch?

    Okay. It looks like Q1 may either be bad or installed backwards. Try flipping it around as a quick check and repeat the test with the 10 kΩ resistor providing base drive to Q1 through the base-emitter junction of Q2. Flipping it around probably won't harm it more than it already is, if it is...
  6. hevans1944

    More efficient LDR "dark" switch?

    How are you going to do that, unless you have one of these: According to the Omegaette HHM93, the 2N3904 that is plugged into it has a beta of 202... whatever that means. I take it to mean this transistor is probably "good"
  7. hevans1944

    More efficient LDR "dark" switch?

    I am somewhat embarrassed to admit that I have reversed the emitter and collector connections on several occasions.:)
  8. hevans1944

    One Way Communication from Chip-to-Chip

    @Pradip Nepali doesn't say so, but he appears to want to transfer inputs on one processor to outputs on the other processor via the serial transmit and receive ports on both processors. Although only two switches and two LEDs (or relays, or whatever) are shown, whatever serial protocol is...
  9. hevans1944

    More efficient LDR "dark" switch?

    If you can't get the LED to turn on and off by varying the pot wiper position, but you measure 1.2 V at the base of the first transistor, that indicates the voltage is the result of two forward-biased transistor junctions connected in series. But it doesn't necessarily mean those are...
  10. hevans1944

    More efficient LDR "dark" switch?

    You didn't change the schematic to reflect the change in resistance value. Can I assume this thing now works? The 2.1 volts should mean both transistors are on and the LEDs are illuminated when the LDR is dark. Is that correct?
  11. hevans1944

    More efficient LDR "dark" switch?

    Yikes! That 100 kΩ pot is loading the hell out of your 3 V battery. Something wrong there. Is it possible you have the pot wired wrong? As a rheostat instead of as a potentiometer, perhaps? When you say "it seems to be fine sweeping from 1.4-ohm to 10k" what does that mean? It's a 100 kΩ pot...
  12. hevans1944

    Remote Controlled Ski

    Let these folks over in Norway do it for you. They know something about skiing.
  13. hevans1944

    More efficient LDR "dark" switch?

    This makes no sense at all. With the 10 kΩ resistor connected to positive terminal of the battery, the other end of 10 kΩ resistor connected to top of potentiometer, bottom of potentiometer connected to emitter of second transistor and negative terminal of the battery, you should now have a...
  14. hevans1944

    More efficient LDR "dark" switch?

    What! You removed the 100 ohm current-limiting resistor in series with the LED! <cringe> What if by some miracle the second BC647 (or 2N3904) goes into saturation because you have managed to zap the base of the first transistor with major voltage? Do this: Remove the 3 V battery. Take the LDR...
  15. hevans1944

    One Way Communication from Chip-to-Chip

    Oh, this is so simple! You already have two identical processors that support serial communications: output on U1-11 (P3.1 TXD) connected with one wire to the input on U2-10 (P3.0 RXD). And you also have input ports for the switches on U1 and output ports for the LEDs or relays on U2. All you...
  16. hevans1944

    Measuring phase between voltage and current(HELP!!)

    Go explore the links provided at your original link. This is an open-source project (free!) that provides all the software you need.
  17. hevans1944

    Measuring phase between voltage and current(HELP!!)

    The Arduino has six (Uno), eight (Mini), or sixteen (Mega) analog input channels. Analog-to-digital conversion rate tops out at about 100 μsec per sample, or about 10,000 samples per second. Using two channels, an effective sampling rate of 5,000 samples per second on each channel could possibly...
  18. hevans1944

    Microcontroller controlled by pushbutton for LED flashlight

    AFAIK, the GPIO pins on the PIC10F20x chips are either inputs, that are isolated (tri-stated) from the GPIO register when the TRIS instruction writes a "1" to that bit, or they are outputs that are in a low-impedance state, whether sourcing current as logical "1" or sinking current as logical...
  19. hevans1944

    Microcontroller controlled by pushbutton for LED flashlight

    Exactly my thought, too. It won't be easy to code this because the switch performs multiple functions and I must periodically check its state to determine how to control the MOSFET. Overall, if the flashlight is off, I can use the awaken-on-pin-change to turn it on for the first 100...
  20. hevans1944

    Microcontroller controlled by pushbutton for LED flashlight

    Today was interesting. I converted my simple "button-push to light an LED" program to put the PIC10F206 to sleep between presses and releases. Took all day to figure that out, and I would still be struggling with it were it not for a program fragment and an explanation I found on the web here...
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