Torben
Well-Known Member
Hi all,
Another question (on my foosball scoreboard, of course) which comes off the end of another thread I had (https://www.electro-tech-online.com/threads/transistor-switching-question.28346/).
The circuit I refer to below is attached.
Basic idea: I am trying to both turn on a 12V/20mA lamp (U1), and trigger a sample from my SPD-20 drum pad. The lamp works fine. (Background: you can trigger the SPD-20 using a piezo directly wired into a trigger input; that's the effect I'm trying to get for my pulse into the SPD-20.) The trouble is that my input pulse is in reality from a 555 configured as a 3-second-on one-shot, which turns on the 3904 controlling the lamp for ~3secs. Oddly, the SPD-20 triggers at the end of the pulse, not the beginning as I would have expected.
In short: someone scores. Immediately, a lamp should light up and a pulse should trigger a sound from the SPD-20. The lamp should stay on for around three seconds. (So far, this all works fine.) The problem is that the SPD-20 is triggered at the end of the three seconds.
(The following paragraph is just background and can be safely skipped.)
I thought it was odd that the SPD-20 would trigger at the falling edge of the pulse, so I first reversed the polarity of the plug into the SPD-20. That achieved the desired effect, until I plugged in the next input and found that both triggered together when they should trigger separately. I tested the SPD-20 trigger inputs (4 of them) with an ohmmeter and found that my original grounds on it had been correct, and I now had my signal inputs connected to SPD-20's common. So I have gone back to the original wiring, which still triggers on the falling edge.
So I tried an RC differentiator: see the second attachment. I figured if I could just get a spike at the leading edge of the 3-second pulse, I'd be golden. No such luck. It still triggered at the end of the pulse. (Note: the 0.6V positive spikes are the result I want; the -1.2V spikes I do not want. Trace Vn007 is from the junction of D2 and R3.) I added the diode D2 to try to get rid of the negative spike generated by the differentiator, but that doesn't appear to work either in the sim or in real life. So I'm lost.
Anybody familiar with SPD-20 triggering, or have any insights into the rookie mistake(s) I'm making here?
Thanks in advance,
Torben
Another question (on my foosball scoreboard, of course) which comes off the end of another thread I had (https://www.electro-tech-online.com/threads/transistor-switching-question.28346/).
The circuit I refer to below is attached.
Basic idea: I am trying to both turn on a 12V/20mA lamp (U1), and trigger a sample from my SPD-20 drum pad. The lamp works fine. (Background: you can trigger the SPD-20 using a piezo directly wired into a trigger input; that's the effect I'm trying to get for my pulse into the SPD-20.) The trouble is that my input pulse is in reality from a 555 configured as a 3-second-on one-shot, which turns on the 3904 controlling the lamp for ~3secs. Oddly, the SPD-20 triggers at the end of the pulse, not the beginning as I would have expected.
In short: someone scores. Immediately, a lamp should light up and a pulse should trigger a sound from the SPD-20. The lamp should stay on for around three seconds. (So far, this all works fine.) The problem is that the SPD-20 is triggered at the end of the three seconds.
(The following paragraph is just background and can be safely skipped.)
I thought it was odd that the SPD-20 would trigger at the falling edge of the pulse, so I first reversed the polarity of the plug into the SPD-20. That achieved the desired effect, until I plugged in the next input and found that both triggered together when they should trigger separately. I tested the SPD-20 trigger inputs (4 of them) with an ohmmeter and found that my original grounds on it had been correct, and I now had my signal inputs connected to SPD-20's common. So I have gone back to the original wiring, which still triggers on the falling edge.
So I tried an RC differentiator: see the second attachment. I figured if I could just get a spike at the leading edge of the 3-second pulse, I'd be golden. No such luck. It still triggered at the end of the pulse. (Note: the 0.6V positive spikes are the result I want; the -1.2V spikes I do not want. Trace Vn007 is from the junction of D2 and R3.) I added the diode D2 to try to get rid of the negative spike generated by the differentiator, but that doesn't appear to work either in the sim or in real life. So I'm lost.
Anybody familiar with SPD-20 triggering, or have any insights into the rookie mistake(s) I'm making here?
Thanks in advance,
Torben
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