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  1. hevans1944

    Designing a Time Delayed Relay

    Kris got both me and John (and perhaps many others) started using PICs. If I could, I would thank him profusely for it postmortem. A few years ago I wanted to get involved again with microprocessors and thought the Texas Instruments MSP430 series would be the way to go. I still like the TI Von...
  2. hevans1944

    LED Signal Dummy load

    Yep. I agree, but let's see if @lxlramlxl has anything more to say.
  3. hevans1944

    How to work with RS485 ?

    Oh, you think? The purpose of college is to teach you how to learn. Your path, if you choose it, to becoming a real engineer has just begun. Sounds like you think that "paper ticket" you get at graduation makes you an electronics engineer. Prepare to be surprised. Among other traits, an...
  4. hevans1944

    Designing Relaxation Oscillator

    This website has a pretty good explanation of UJT operation. If you load Vout with an LED, the timing will be affected.
  5. hevans1944

    Upload code from pic

    IF the security bit IS NOT SET, you can download the code from the PIC using your PICkit 3. That's a crap shoot for a commercial product. Why wouldn't the manufacturer lock their code? I would if it were mine.
  6. hevans1944

    LED Signal Dummy load

    For those of us not familiar with British Railroad wiring documentation, this reference will help to understand the wiring diagram @lxlramlxl posted. BTW, @CDRIVE, everything in the dashed-outline box is part of the now-obsolete SL35 incandescent lamp signal head and it is not part of the...
  7. hevans1944

    LED Signal Dummy load

    Only one proving relay to service two or more lamps? How exactly does this work? Are all the lamps wired in common to this one source of power (through the proving relay coil) and then switched independently on their other end to the power supply common to determine which light will illuminate...
  8. hevans1944

    blowing fuses

    What a hatchet job! It looks like the aftermarket light is really two lights, each independently operated from a pair of AA cells. Two cells operate the light on the left and two more cells operate the light on the right. So, only 3 V is applied to each light via the central switch mechanism...
  9. hevans1944

    LED Signal Dummy load

    Ah! Finally a new schematic from Chris in post #33, and a better one still in post #37. Thank you, Chris. These are much better circuits than what I was thinking of because the LED now actually does something useful, i.e., it lights up when 300 mA of current is drawn through the probes. As...
  10. hevans1944

    LED Signal Dummy load

    YES. All are required. You need a dummy load circuit for each signal-head load you are testing. That circuit consists of a 400 Ω 50 W power resistor connected to your test leads with the croc-clips. This power resistor is also connected in parallel with three other components that are connected...
  11. hevans1944

    hardware learning

    If you are currently employed in an area using electronics design, the best thing you could do is find a mentor to direct you. I was very fortunate to have a mentor when I started my career, a fellow employee super-technician who did engineering design without a college degree. His most...
  12. hevans1944

    LED Signal Dummy load

    The relay has a 30 Ω coil and drops about 9 VAC across the coil when 300 mA flows through the coil from the signal head LED load. The relay is used to verify that the signal head actually draws its rated current and is not defective because an LED string in the signal head is open. Because the...
  13. hevans1944

    LED Signal Dummy load

    Okay, I think I see what you are trying to do now. In post #5 you stated: "you would croc-clip on the circuit to some links. In reality or you would have is a resistor and an LED in series with clips on either end to put on the positive and negative feed to represent a load." So the resistor...
  14. hevans1944

    Voltage Divider to control Current in a Circuit

    Yep. That's especially important multiple, super-duper, high-current, re-chargeable Li-ion batteries like the IMR 18650. You need a battery management circuit to keep everything balanced, especially while charging.
  15. hevans1944

    LED Signal Dummy load

    Yeah, a 40 watt glass light bulb is not what I want to stuff into my go-to bag. So LED it is. You need to find an LED that will pass 300 mA through the relay to simulate the signal head load. Most LEDs are rated at much lower currents, on the order of 10 mA or so. You could parallel a single...
  16. hevans1944

    LED Signal Dummy load

    Nah, my only contact with railroads is I once traveled from California to Pennsylvania with a stop in Chicago while returning via steamship from Okinawa in the 1950s. i was a lot younger then so I didn't really appreciate the ride as much as I would today. Unlike India, the US rail system...
  17. hevans1944

    Voltage Divider to control Current in a Circuit

    Wiring batteries (or cells) in parallel is risky business. The one with the greater charge will discharge into the other one. Sort of like getting a battery-jump to start your car. Works for a short while. Best to do as @BobK suggested: two cells in series with an efficient buck converter to get...
  18. hevans1944

    LED Signal Dummy load

    This thread appears to be related to Indian rail systems, specifically the LED signals used to safely direct the train engineer along the tracks. The nomenclature used for the relays may be unfamiliar. For example, the "back contacts" refer to normally-closed contacts when the relay coil is...
  19. hevans1944

    Today's Salvage Haul

    I really love getting (even inexpensive) parts for no investment other than sweat equity. Now go have some (more) fun!
  20. hevans1944

    Grounding and Circuit Noise

    So, you are not trying to put lip-stick on a pig! More like "tuning" the fine points of an acceptable design that has, perhaps, some room for improvement. Said improvement being part of the next phase when someone starts throwing more money at it. Been there, done that, sometimes was awarded a...
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