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A push-button for reversing polarity?

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dw2296

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Hi,

I am an amateur working on an electronics project and am using a latching relay that requires a reversed polarity to unlatch. I know that I can use a DPDT rocker switch and wire it to reverse polarity, but I really want to use a push button for this specific application. However, it has to be momentary and normally off when not in use; I just want it to momentarily pulse the relay in directions that are reversed every time the switch is pressed (so for example with five succinct presses of the push button the relay would go something like: latch, unlatch, latch, unlatch, latch). Is this possible? I've been searching online for something like this but haven't had any luck so far. Any suggestions to accomplish the same task in a slightly different way is also welcomed. Thanks for any help!

If it matters, I am using the relay below. One side of the relay has a single throw circuit and the other has a dual throw circuit, while the two opposite pins at the end control it.

https://www.ebay.com/itm/271807339723?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT
 

jiripolivka

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I have designed a driver circuit for a similar latching relay. I do not remember details, but I used a 7401 IC to form pulses from the push button, then a divider-by-two, and a pair of optical power drivers, PVG 612, to drive the coil(s) in both directions.
To avoid an isolated DC power supply, for reversed pulses I used a small DC-DC converter to charge two 50 uF capacitors which then were discharged through the latching coil. Capacitors were charged through 1k resistors as only pulses were sent to the coil. Depends how fast the switching operation is required.

If you need only one switch, I would prefer the manual toggle switch. It would replace all above complex circuitry and work reliably. My circuit was needed as the customer wanted to use either a local push button, or remote logic input.
 

SunnySkyguy

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You would just need a toggle Flip Flop, a one shot and two active low switches with Relay coil common to V+.

Single push button goes to one shot which debounces push button and drives FF Clock input in /2 mode or toggle mode ( D=Qbar)

Q AND one shot = Gate drive 1
Qnot NOR one shot = Gate drive 2
FETs would be N Ch enhancement type.. most common. with RdsON<< Coil Rs.
AND function could be done in logic or inverted inputs with Diode OR and R pullup.

Make sense?

Here's proof concept.
Click on the switch bar.

Momentary switch should be gold plated signal type. (non-oxidizing low current)
FETs can be any RdsOn << Load Rs. Add reverse clamp diodes to coils.

This is a non-retriggerable one shot, leading edge of push button, and variable duration set by RC with Schottky signal diode to reset cap fast.
8007254800_1442669809.jpg

Scope traces show switch, Power in each coil (dummy 100R) and complementary toggle states.
 

dw2296

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Thanks guys, the stuff you've given me is great. I think I'll definitely look back at these setups if I have to, but I'll probably go with a toggle or rocker just for the simplicity.
 

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