Anyone have experience with an RC driven temporary "ON" transistor switch?

[harp]

One rapid LED light pulse per press of push button switch circuit using 2N3904 NPN BJT

Just adjust capacitor to desired time interval, like 10uF or 22uF...

[truclacicr]

Changes as said is to swap the 33K and 47µF capacitor. Lose the 1k resistor, not needed and interferes with operation.

I would use a resistor in the base circuit to limit the B-E voltage. The capacitor is initially discharged, so the base could see as much as 5V immediately after power-on.

[redwire]

Latching relays need only a brief blip to their coil. Panasonic, Omron G6AK need 10msec pulse. Note that if you bang or bump the relay, it can unlatch so your firmware must bump it and never assume the relay is where you left it.
Had a voltmeter product people would drop and unlatch the range relays so it would then read stupid and get back for repair to our shop.

OP is basically looking for a power-on reset circuit and there are 1,000 ways to skin that cat.

[eccerr0r]

I would use a resistor in the base circuit to limit the B-E voltage. The capacitor is initially discharged, so the base could see as much as 5V immediately after power-on.

correct, it should be in series not in parallel, alas, at 3.3V rail and the charge time, it shouldn't be too long until it's charged and shut off.

TBH dangit, i'm too used to cmos and ttl devices where input current limiting is implicit/built-in...aaaahhh...

Latching relays need only a brief blip to their coil. Panasonic, Omron G6AK need 10msec pulse. Note that if you bang or bump the relay, it can unlatch so your firmware must bump it and never assume the relay is where you left it.
Had a voltmeter product people would drop and unlatch the range relays so it would then read stupid and get back for repair to our shop.

OP is basically looking for a power-on reset circuit and there are 1,000 ways to skin that cat.

Dammit I need to fix my Tek scope, one of the latching relays in it is stuck... *sigh* Not sure why Tek decided to use latching relays in their attenuators...

[stj]

the scope probably uses latching relays to avoid any inductive coupling from a coil and the signal

[redwire]

[...] Dammit I need to fix my Tek scope, one of the latching relays in it is stuck... *sigh* Not sure why Tek decided to use latching relays in their attenuators...

Latching relays are used where you want to save power, not have a coil energized all the time, like in battery-powered gear.
Also in precision voltage measuring gear, you don't want a relay heating up and adding a thermal EMF potential due to the dissimilar metals and thermocouple junctions inside a relay. So you'll see them in high end bench multimeters too.


If a relay (or reed switch) is sticking, I find it's because they get magnetized in one (pole) direction with age, the only one polarity they work in.
I will use an old cassette-tape head demagnetizer, or energize the coil backwards (out of circuit) to fix them. Not sure why but it works. I think some relays though have a bias magnet to make them more sensitive so then AC field would wreck that. Not sure.

[eccerr0r]

Yeah it's a line powered scope. The coupling problem seems sound but if it's driven by a DC signal, it should also be stable...