Author Topic: MOMENTARY GROUND - Latching SPDT creates momentary effect both ways  (Read 204 times)

stonerbox

Would this work? I threw this together with the intention to pull the voltage at R25 (3k) momentarily to ground every time the SPDT switch is pressed. I tested with a LED's cathode connected to the collector and it lights up shortly with each press of the switch but I am uncertain if the circuit is good as is?

"JFETs are like people.... similar,  but different from one another."
- BubbaFet

PRR

Re: MOMENTARY GROUND - Latching SPDT creates momentary effect both ways
« Reply #1 on: September 14, 2021, 04:05:31 PM »


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stonerbox

Re: MOMENTARY GROUND - Latching SPDT creates momentary effect both ways
« Reply #2 on: September 14, 2021, 04:08:51 PM »


?

But that would not make it momentary. The voltage must be able to quickly rise again.
« Last Edit: September 14, 2021, 04:11:53 PM by stonerbox »
"JFETs are like people.... similar,  but different from one another."
- BubbaFet

antonis

Re: MOMENTARY GROUND - Latching SPDT creates momentary effect both ways
« Reply #3 on: September 14, 2021, 05:07:12 PM »
The voltage must be able to quickly rise again.

As soon as you release the switch button.. :icon_wink:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

stonerbox

Re: MOMENTARY GROUND - Latching SPDT creates momentary effect both ways
« Reply #4 on: September 14, 2021, 05:24:31 PM »
The voltage must be able to quickly rise again.

As soon as you release the switch button.. :icon_wink:

Sorry if I explained this poorly in the initial post. If the switch was momentary yes but I am using a latching switch.
« Last Edit: September 14, 2021, 05:45:25 PM by stonerbox »
"JFETs are like people.... similar,  but different from one another."
- BubbaFet

anotherjim

Re: MOMENTARY GROUND - Latching SPDT creates momentary effect both ways
« Reply #5 on: September 15, 2021, 04:47:19 PM »
The problem with the circuit is that once the switch is used to send +v to the timing cap C10 it will be charged and won't discharge when switched to 0v - there is no path as Q1 b-e junction is reverse biased. You would put a reverse diode across Q1 b-e junction to provide a discharge path - but that won't pulse Q1 on - that won't be possible.
Croeso i Diystompboxes.

If they didn't hear you then you didn't say it.

antonis

Re: MOMENTARY GROUND - Latching SPDT creates momentary effect both ways
« Reply #6 on: September 15, 2021, 04:55:34 PM »
timing cap C10

I shouldn't implement a 47pF cap for that use..
(47nF with proper resistor scaling, perhaps - 470nF, more realistic ..)
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

ElectricDruid

Re: MOMENTARY GROUND - Latching SPDT creates momentary effect both ways
« Reply #7 on: September 15, 2021, 07:08:38 PM »
Can you explain why are you trying to use a latching switch for a momentary job?

It seems like an odd choice!