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# convert on/off input to seperate momentary pulses

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#### *M2*

##### New Member
I am trying to get a DC input to pulse two different relays when it goes high or low.

DC input = low then goes high: relay one pulses for 1 second
DC input = high then goes low: relay two pulses for 1 second

I found a 555 timer circuit that will pulse when it goes high (half of what I need), but I need it to pulse separate output when going low.

trigger circuit

Basically, I need it to duplicate this operation on the trailing edge of the clock signal as well but on a different output.

I have a handful of 555s and 556s at my disposal.

I am trying to get a DC input to pulse two different relays when it goes high or low.

DC input = low then goes high: relay one pulses for 1 second
DC input = high then goes low: relay two pulses for 1 second

I found a 555 timer circuit that will pulse when it goes high (half of what I need), but I need it to pulse separate output when going low.

trigger circuit

Basically, I need it to duplicate this operation on the trailing edge of the clock signal as well but on a different output.

I have a handful of 555s and 556s at my disposal.

Use the same circuit again for the second purpose and tap the input from the same above input signal , give it to a NOT gate or (shorted NAND)...then feed to the circuit....it would solve your problem...

such a simple solution! I should have thought of that. My idea was much more complicated. Using a 556 then will make it a small, simple circuit!

Thank you!

What is the voltage and current available from the power supply being pulsed?

What voltage relays do you want to use?

What is their coil resistance?

Should the relays be powered from the same power supply as is being pulsed?

What is the turn-on time of the supply being pulsed?

Here's one principle.

You need a XOR gate and a delay circuit. This delay circuit could consist of a RC and a Window Detector Circuit (WDC). The WDC kinda works like a schmitt-trigger but input levels can be adjusted to any needs.

God luck

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What is the voltage and current available from the power supply being pulsed?

What voltage relays do you want to use?

What is their coil resistance?

I haven't picked relays yet. I would assume I need 12vdc coils. Contacts will trigger an existing 24VAC GE RR7 relay. The relay controls a 20A 120VAC circuit. It has two coils. One gets energized close contacts, the other coil gets energized to open contacts. Coil inputs are montary, and relay contacts' state is latching. These are controlled currently by two momentary rotary dials, one for On, one for Off. I am trying to control them by low voltage DC via a DMX controller. When I want the lights on, DMX channel output will be 10vdc constant, lights off 0vdc constant. Here is image of current control method: **broken link removed**

Should the relays be powered from the same power supply as is being pulsed?

What is the turn-on time of the supply being pulsed?
Relays are going to switch 24VAC which is always hot, but coils can be powered by 12vdc provided by this circuit's supply
Not sure what you mean by turn on time.

It has been a while since i designed a circuit... so it is all starting to come back to me slowly.

With Rajaneesh's advice, I will be able to build the control circuit, but by all means, I welcome the advice on the relays and how to power them to reduce noise, power consumption, etc.

I haven't picked relays yet. I would assume I need 12vdc coils. Contacts will trigger an existing 24VAC GE RR7 relay. The relay controls a 20A 120VAC circuit. It has two coils. One gets energized close contacts, the other coil gets energized to open contacts. Coil inputs are montary, and relay contacts' state is latching. These are controlled currently by two momentary rotary dials, one for On, one for Off. I am trying to control them by low voltage DC via a DMX controller. When I want the lights on, DMX channel output will be 10vdc constant, lights off 0vdc constant. Here is image of current control method: **broken link removed**

Relays are going to switch 24VAC which is always hot, but coils can be powered by 12vdc provided by this circuit's supply
Not sure what you mean by turn on time.

It has been a while since i designed a circuit... so it is all starting to come back to me slowly.

With Rajaneesh's advice, I will be able to build the control circuit, but by all means, I welcome the advice on the relays and how to power them to reduce noise, power consumption, etc.

As far the relay selection is concerned, you are not going to drive the real load directly. You need to trigger the existing load control relay (GE) which has 24V AC coil. So the consumption of the coil will be very low. (in few hundred mA range)
So if you have onboard 12V dc available, go for 12V DC coil with 5A contact SPST relay...have a look at GOODSKY sugar cube miniature DC relays.....

Put a freewheeling diode across the relay to arrest the switching noise....injecting back to the controller...

Hope this help....

Here is a circuit that may work for you. It uses two 12Vdc relays with a coil resistance of >=100Ω.

The ON relay pulses for about ~1s when the SPST switch closes (rising edge of the 12V IN signal. The OFF relay pulses for ~1s when the switch opens (trailing edge of the IN signal). It is powered with a 12V DC supply that stays on (otherwise there would be no power to pulse the OFF relay).

You can wire the contacts of the two relays to the 24Vac in your system.

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Or even a little more simple. Opps! missed the need for a second relay out.

Ken

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Here is a simplified version of the one I posted above. It doesn't require an unbroken connection to the 12V power supply. It stores the energy required to pulse the OFF relay in a larger capacitor, which also pulses the ON relay when Power is first applied.

C1 is big!, however, if you can find some sensitive 12V relays you could make it smaller. The sim was done with 100Ω relays, so if you could find some 400Ω ones, you could reduce C1 to ~2200uF. Note C1's polarity.

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