Alternating relays momentary closure

[LKO Railroad]

I have an application where a twin coil (15V 2A) latching solenoid needs to be controlled with a single momentary switch. Press once to move the solenoid left, press again to move the solenoid right.

Here is what I have come up with. A flip flop connected to edge triggered non-retriggerable monostables. Pressing the switch causes relay #1 to close for a brief period and then open. Pressing the switch again causes relay #2 to close for a brief period and then open.

Before I breadboard this I kindly ask your opinion. Think it will work?

 

[AnalogKid]

I have a circuit from another thread that does all of that with one hex inverter.

This is much less work:

 

[LKO Railroad]

Because the relay action has to be momentary. Both relays are open except for a brief period when either of the relays closes to provide a pulse to the respective solenoid. The solenoid coils are not suitable for continuous duty.

 

[AnalogKid]

Sorry, I misread your first post and thought the twin-coil latching thing was a relay. oops. I'll look for my other circuit.

ak

 

[AnalogKid]

More thoughts...

1. If you use the button press as the timer for the relay coils, you eliminate both monostables and replace them with gating. Now it's just one toggle and some NAND gates.

2. BUT - If one end of the switch does not have to be grounded, now it's just one CD4093, two 2N4403s, and no relays. I suppose I should ask, what is the solenoid current?

If the current through the solenoids can be reversed (+V common, two coils switched to GND) things become even more simple.

ak

 

[LKO Railroad]

Solenoid current is 2A @15V.
Solenoid current cannot be run through the switch. Also, want option to add additional switches should the need arise to control from more than one location.

one toggle and some NAND gates

I don't understand how a momentary relay action could be achieved without a timer of some sorts.

 

[AnalogKid]

I don't understand how a momentary relay action could be achieved without a timer of some sorts.

That was based on running the solenoid current through the switch.

Can the solenoid coils be pulled to GND? This makes it easier for the solenoid voltage to be different from the circuit voltage.

ak

 

[LKO Railroad]

The solenoid coils are energized with a huge unregulated power supply that also supplies power to other non-related equipment. It is nothing more than a transformer and bridge rectifier. It is impractical to change the solenoid power supply. There are multiple instances of the solenoids.

Inserting a relay into the supply lines is about all that I can realistically do. That is why I designed the circuit to be independent of the solenoid wiring.

 

[AnalogKid]

Unfortunate, but not a deal breaker. It comes down to availability and reliability. Which is better for you, two relays with contacts rated for at least 4 A DC, or two power darlington transistors (TIP125)?

BTW, I wasn't suggesting changing the solenoid power supply, just the connections to it.

ak

 

[LKO Railroad]

I went the relay route for 100% isolation from the solenoid circuit.

 

[AnalogKid]

First pass. Since all gates are acting as inverters, the 4093 can be replaced by a Schmitt-input hex inverter such as a CD40106. If the relay coil current is below 100 mA -ish, R5/Q1 and R6/Q2 can be replaced by 2N7002's.

Multiple switches can be connected in parallel with SW1. Use twisted pairs for connections, shielded if possible.

The pulse formers are the same as in your schematic, but I question if 100 ms is long enough to activate the relays or the solenoids.

ak

 

[AnalogKid]

I just noticed that in your original schematic the 4013 flipflop does not toggle. To do so, the -Q output is connected to the D input. Also, there is no switch debouncing.

ak

 

[LKO Railroad]

That certainly is a much more elegant solution than mine. Thank you.

To increase the relay activation time to about 1/4 second does 2.2uF for C3 & C4 sound right?

Here is my updated circuit with a JK FF and debouncing. Although compared to your solution mine seems overly complex.

 

[AnalogKid]

Because your circuit drives the timers with latched outputs, there is no reason for a true monostable. A simple pulse differentiator gets you the same output pulse width for the same components. Since you have one gate in there, one more gate can replace each 4538 section and eliminate the chip.

If 1/4 sec. is long enough, then 2.2 uF sounds fine.

ak

 

[LKO Railroad]

I like your solution better. I will try it first.

 

[LKO Railroad]

@AnalogKid - Stopped back to say thank you. Your circuit worked well. Some trial and err was necessary with the RC to get the relay close time right (as you predicted). Thanks again.

 

[AnalogKid]

Great news, glad it worked out. Can you post your final schematic?

ak

 

[LKO Railroad]

The same schematic you posted above.