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Recent content by MitchSF

  1. MitchSF

    Help with transistor relay switch

    I can't change the 12v connection to the horn relay. Even with the added transistor, the same thing happens because the circuit is still powered with 12v through the horn relay. The easiest way at this point, I think, is to add a small 12v relay on the output, to isolate the relay coil. I'd...
  2. MitchSF

    Help with transistor relay switch

    On second thought, I think it would be a PNP, with emitter to the relay wire, and collector to ground. Mitch
  3. MitchSF

    Help with transistor relay switch

    It worked! I calibrated it on the bench with a 150 ohm resistor on the input using the 10k variable pot, and it worked fine in the car. Steering wheel switches worked perfectly, and the 200 ohm switch did not close the horn relay. Now the last problem - the horn honks when the ignition is...
  4. MitchSF

    Help with transistor relay switch

    I'll try this later today or tomorrow. I can always change the 220 to something higher, if it doesn't work. Thanks again, Mitch
  5. MitchSF

    Help with transistor relay switch

    Hi, no problem. Thanks again for the help. There is a very small current on the input to the Peripheral Electronics module, a few milliamps, at around 10 volts, so I don't have to supply the voltage. The switch assembly simply switches each resistor to ground, and the horn switch grounds the...
  6. MitchSF

    Help with transistor relay switch

    Here are the resistor values that are grounded from each switch: 220 ohms 600 1300 1600 2800 direct ground (horn) I can change the 220 and 600 ohm resistors to some higher value. The Peripheral Electronics module trains itself to associate resistor values that it reads with infrared commands...
  7. MitchSF

    Help with transistor relay switch

    I'll try this later today. I want to be clear on a couple things - the zener goes from ground to one input, and a 5-47k resistor goes from the same input to 12v. The sense input goes through a 47k resistor. I still don't see why the relay won't close if this sense input is grounded through a...
  8. MitchSF

    Help with transistor relay switch

    I can try the LM339 tomorrow, since they're available at Radio Shack. I'm a software guy, not an EE, so I'm a little slow with this stuff. Please let me know if this is correct: LM339 inputs are + and -. I guess you connect the + to 12v through the zener, and - to the switches that ground...
  9. MitchSF

    Help with transistor relay switch

    I'll do that when the ic's arrive. How would I incorporate a delay? If this circuit doesn't work, I know I can use a Basic Stamp to accomplish this. The input will go to one I/O pin and I can use the RCTIME function to read the resistance (indirectly, but it will work), and six I/O's for...
  10. MitchSF

    Help with transistor relay switch

    I tried the zener diode in series with the base, and it still doesn't work. I did make one mistake - the lowest resistance is 200 ohms, not 500, so the circuit should not respond unless it sees a ground, or something very close. Also, the circuit is triggered on power up, so the horn honks...
  11. MitchSF

    Help with transistor relay switch

    Since the relay is already connected to +12v somewhere in the car, I connected the other side of the relay to the emitter of the PNP transistor, and the collector to ground. I'll try a zener diode in series with a 20k resistor between the base and the wire that senses resistance from the...
  12. MitchSF

    Help with transistor relay switch

    I think I can do this now. I'll use a NOR gate, so that when the input is grounded, the output will turn on an NPN transistor. I haven't been able to find out what resistance to ground a CMOS gate's input needs, in order to trigger. Hopefully it's much less than 500 ohms, or this won't work...
  13. MitchSF

    Help with transistor relay switch

    Thanks, guys. Skogsgurra, I tried exactly that a couple hours ago, except I used 5k in series with the base, and 33k from base to 12v. I have no idea if this is necessary. It worked on the table, but not in the car. I think what you mentioned about reducing the resistance by the gain of...
  14. MitchSF

    Help with transistor relay switch

    I built the circuit today, and it works, but not the way I expected. When I ground the input, nothing happens. But when I connect it to 12v or even a lower voltage like 6v (I'm using two 6v batteries to test), the relay closes. I need it to close when the input is grounded. Did I wire it...
  15. MitchSF

    Help with transistor relay switch

    I forgot to mention that the horn relay is already connected to +12v, and the side that I have in the steering wheel is the other side of the coil, which gets grounded to sound the horn. I don't know if this matters. I'll try to breadboard the circuit this weekend. Thanks again, Mitch
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