I have a 5V control signal; high is on. I'd like to be able to vary the time between the signal going high and when it appears at the base of a transistor being used to control a current. Any suggestions for that? I was thinking of something that used a pot or a variable cap to adjust the delay.
Stephen
How much of a delay are you talking about ?
A 555 timer and an AND gate should do the trick.
don
PS: Google is your friend.
On a sunny day (Sat, 22 Aug 2009 10:44:01 -0700 (PDT)) it happened Stephen-I-am wrote in :
_______ | | diode | | _ k a _ signal | | | | | | | | A
0V ---- - --- R ------------ + | out --- B === --- - | C | opamp /// | | | . 0 to 5 V . | control signal A . | ------------ . |------ --------
----- | | B | |
--------- -----------
This should do it:
PNP +5 V -----------------------+--------- --- + Output | e\\ /c [220R] --- | | +---[1K]---+ Signal --[POT]--+ | | | ----- +----+---[1K]---/ \\ TL431 | | --- R1 [100K] [C1] | | | | Gnd--------+----+-----------+
As C1 charges it raises the voltage applied through the 1K to the TL431. When it reaches ~ 2.5 volts, the TL431 turns on and the PNP conducts. The pot setting and C1 value determine the delay between the rise of Signal and the rise of Output. Output will drop after Signal drops - R1 sets the time for the cap to discharge and thus the output to drop. If a faster dropout is needed, put a PNP across C1 with the collector grounded and the base through 1K to the emitter.
Ed
How about just an AND gate and a variable R with a C?
John
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