🚀 go-pugleaf

First, I want to thank everyone for their help.

Here are the reponses I received, and a revised circuit I intend to build,
(Thanks, Mr. Koch!)...

>> From: uunet!mlb.semi.harris.com!jws (James W. Swonger)
>>
>> If you're going to all the trouble of putting discrete components 
>> together, why not use a good 'ole 555 instead? They're tough and can
>> be set up for monostable (one-shot) operation. They also are cheaper than
>> most transistors.

Mr. Swonger, almost the whole circuit is for driving the relay. Only the
first capacitor, and resistor are for the timing. By adding a 555, I would
mabey need to add another resistor, and still need the power transistors...


>> From: grege@gold.GVG.TEK.COM (Greg Ebert)
>>
>> You are using a common-collector configuration. The load is at the emitter,
>> and is 3 base-emitter voltage drops below your input voltage, which is
>> at most 5 volts (TTL). Thus, the maximum voltage across the relay is about
>> 3 volts. Note: the 2N2222 causes 1 VBE drop, the TIP120 causes 2 VBE drops
>> because it's a darlington. I'll bet you don't even need the 2N2222 because
>> the DC beta of a darlington is very high, maybe 5000 to 10000.
>> 
>> Your circuit will work correctly if you place the relay between +12 volts, 
>> and the collector of the TIP120, then ground the emitter of the TIP120. It 
>> takes an additional splice, but it will work.
>> 
>> You will have to clamp the inductive load from the relay by connecting  diode
>> directly across the relay, with the CATHODE going to the + 12V supply.
>> 
>> Caveat: You are running on an automotive electrical system which is known to
>> have beastly voltage transients!!
>> 

Mr. Ebert, Thanks for your insight.. A couple of points... I am aware that
my circuit has a good chance of working if I ran the relay directly to +12,
but I would rather leave it as it is. The reason is for safety (less +12
running around), I can put it back to original if I want to easier, and
because I also want to connect things like parking lights, which would need
the same configuration (since they are also grounded).

I forgot to mention, that there is already a diode connected inside the
relays, according to the schematic, as you say. As for the spikes, and all
that... haven't had a problem yet! The Radio Shack model 100 has a very
forgiving power supply that I run off another +6 regulator. Even when I
drained the battery, and proceeded to make a very hostile environment with
attempting to start the car (nearly a short, I would guess at that level)
didn't phase it. I has an internal NiCd to keep it's memory.

>> From: ico.isc.com!uunet!motcid!ivory!koch@mps.ohio-state.edu (Clifton Koch)
>>
>> Try this:  Connect the emitter of the 2n2222 to ground and the collector
>> to the 100 ohm resistor (remove the 1K resistor).  Replace the TIP 120 with
>> a PNP power transistor with the emmiter going to +12 and the collector to
>> the relay.  Insert a resistor (try about 10K) between the 47uf cap and the
>> base of the 2n2222.
>> 
>> What this will do:  When the +5 signal is applied to the cap, the other side
>> will go to +5 and decay from the current going through the 100K and the 1K
                                                                 [gone now ^^]
>> and base of the transistor.  The current through the 10K will turn the 2n2222
>> on which will allow current to flow from the PNP base turning that transistor
>> on, energising the relay.  When the 47uf decays to ~.7v the NPN transistor
>> will shut off, shutting off the PNP transistor, shutting off the relay.
>> 
>> I doubt that you'll need a darlington transistor, but it doesn't matter much.
>> You'll probably have to play with the '10K' value to get the time constant
>> you're looking for (or the cap value).  Remember to put a supression diode
>> across the coil (1n4004 is a good choice) or your output transistor won't
>> last long and probably will burn out the door solenoids.
>> 
>> I've used this circuit or something similar for quite a few automotive 
>> projects with no problems.
>>
>> Cliff Koch

Thanks again Mr. Koch! Now, following Mr. Koch's recommendations, here is the 
modified circuit I will test when I get my next chance... I think I will use a
TIP125. On the card the TIP120 came on, they say that this is it's complement.
I know this may be overkill, but since I don't have proper equipment to check 
on such things, I'd rather be safe. One question... Is the 100 ohm resistor all 
I need between the 2N2222, and the TIP125? I seems to me that I might need a 
resistor here to +5 to supply current to the TIP125, when the 2N2222 is not 
grounding it. I may be wrong! Also, I may also want to use this circuit to 
power my parking lights... I assume that replacing the relay with about 5 
incandescent lamps will work just as well...

                      _____  ,-----.
  47uF               /     \/ C    |
  +| |            B | |  /  |      |
>--| |---.--\/\/\/--|-|<    |      |           |-------| E
   | |   >    10K   | |  \| |E     |         B |       |--- +12   existing relay
        <            \_____/\__.   `-/\/\/\/---|       |          ______ /
         >            2N2222   |       100     |       |__________nnnnnn___
    R1  <                      |               |-------| C     `---|<------|
   100K  >                     |                TIP125                     |
         |                     |            (PNP darlington)             -----
       ------                -----                                        ---
        ---                   ---                                          -
         -                     -

>> From: uunet!motcid!violet!reichert (Charles H. Reicher)
>> 
>>	Try adding a series diode (1N4148, etc.) with the 47uf capacitor, 
>> cathode (Banded end, arrow pointing to 2N2222 Base) and a 1 to 10uf capacitor
>> from 2N2222 Base to Ground, positive end at base.  This will allow the base 
>> to hold a charge while the diode prevents discharge back thru the 47uf cap.
>> I'm assuming you only want to activate the Relay a short time!
>> 
>> 73's  Chuck Reichert KD9JQ

Thanks, Mr. Reichert. I may also try this good suggestion.


Thanks again for everyone's help!

Christopher A. Nielsen
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