Solid State relay and timer circuit

Thread Starter

Tutor88

Joined Feb 8, 2023
117
I’m experimenting with an SPDT solid state relay (LCC120) and a timing circuit based on a 4060BE, as a student demonstration, and seeing how a 12V signal can be routed to an alternative path using a short pulse (12V, ~5ms). The circuit is as shown.

Forum Circuit.pngI want the relay to trigger, to change which output the input is connected to, when the trigger pulse arrives and then to remain that way for a short adjustable period of 30-200ms before reverting to the original output. The outputs will light LEDs and so for most of the time the LED connected to Output 1 will be on and then, after the trigger pulse arrives, the other LED will be on for the set duration before the relay flips back again.

My question is about how to use a 4060-decade counter to achieve this switching. The 4060 puts out a high after a set interval, based on its oscillator frequency and the chosen Q output, whereas I need to maintain the initial trigger high to keep the relay flipped and then a low after the preset interval for it to revert.

Perhaps I can use the 'Reset' input 12 as a sort of enable or I can’t use this and I need some form of latching relay instead but I haven’t found one in the small Dip 8 format like the LCC120.

Any ideas?
 

StefanZe

Joined Nov 6, 2019
191
Whitout a resistor on the input of the LCC120 you will exceed the maximum input current.
Do you have to use the CD4060? Something like a NE555 would probably be a better solution.
 

Thread Starter

Tutor88

Joined Feb 8, 2023
117
Yes a resistor there will be required. At the moment I'm sorting the principle of operation.
I'm happy to use a 555 so can you suggest a circuit? Won't I still have the same issue about how to keep the trigger pulse high to keep the relay switched until the end of the set period?
 

Thread Starter

Tutor88

Joined Feb 8, 2023
117
Ok, let me run through the operation so I can understand what's going on.

In place of the press button, my trigger pulse comes in on Pin 2 which sends the output on Pin 3 high and flips the relay's outputs. This state remains for a duration set by the values of C1 and R1 (which I would need to make adjustable) after which Pin 3 goes low again and the relay reverts. If that's the sequence then I will draw up my version of it and post it later.

Thank you
 

StefanZe

Joined Nov 6, 2019
191
Yes, just one small detail. The trigger pulse on Pin2 is a low pulse (a transition from high to low will start the time).
You can use a n-MOSFET instead of the button in the circuit i showed you to invert your trigger signal
 

LowQCab

Joined Nov 6, 2012
4,064
A standard PWM Circuit using a Dual Op-Amp, or a Comparitor, is my vote.

This will provide simple wide-range Frequency-Control with the addition of a Pot in place of
the 10K Resistor feeding the Capacitor,
and can create any Mark-to-Space-Ratio desired with a 3 to 7-Volt Input,
( shown as a Pot in the Schematic ).
.
.
.
PWM Comparitor .PNG
 

StefanZe

Joined Nov 6, 2019
191
A standard PWM Circuit using a Dual Op-Amp is my vote.
This will provide simple Frequency-Control with the addition of a Pot in place of
the 10K Resistor feeding the Capacitor,
and can create any Mark-to-Space-Ratio desired with a 3 to 7-Volt Input,
( shown as a Pot in the Schematic ).
.
.
.
View attachment 287264
This will switch the outputs all the time. Read the frist post again. OP wants a single shot pulse with variable length after a trigger pulse. Your circuit does not do that
 

Thread Starter

Tutor88

Joined Feb 8, 2023
117
My trigger pulses will be arriving every 0.5s (2Hz) so the sequence I described will be repeating until the power goes off. I'm drawing up the 555 option at the mo.
 

Thread Starter

Tutor88

Joined Feb 8, 2023
117
Ok here is my proposed circuit but I have a few Qs underneath:

My relay circuit.pngI don't think I have the trigger inverting right since when the trigger pulse arrives at the FET Gate, will it pull down Vcc enough at pin 2 to cause the 555 to start, and will it interfere with the RESET on pin 4? I doubt Vcc will be influenced enough by the FET turning on so I expect that's not quite right.

The 555 output on Pin 3 is suggested to be only 1-2V so will that be enough to operate the LCC120?

I have calculated the adjustable R2 values to give me an ON period of about 20-300ms.

Thanks
 

StefanZe

Joined Nov 6, 2019
191
Ok here is my proposed circuit but I have a few Qs underneath:

View attachment 287269I don't think I have the trigger inverting right since when the trigger pulse arrives at the FET Gate, will it pull down Vcc enough at pin 2 to cause the 555 to start, and will it interfere with the RESET on pin 4? I doubt Vcc will be influenced enough by the FET turning on so I expect that's not quite right.

The 555 output on Pin 3 is suggested to be only 1-2V so will that be enough to operate the LCC120?

I have calculated the adjustable R2 values to give me an ON period of about 20-300ms.

Thanks
You need a pull-up resistor between pin 2 and VCC (R3 in the circuit I sent you earlier). Without the pull-up resistor you short circuit the supply voltage.

~2V is the low level outputvoltage of the NE555 the high level outputvoltage is around Vcc-2V.
 

Thread Starter

Tutor88

Joined Feb 8, 2023
117
Oops, not desirable! I knew something wasn't right. . . .

My pulse relay circuit.pngIf this is now ok I will set it up on a breadboard once the parts are in.

Thanks
 

StefanZe

Joined Nov 6, 2019
191
Looks ok. R4 should probably a little bit higher (around 2k), so the current for the input of the lcc120 is not too high (See datsheet)
 
Last edited:

Thread Starter

Tutor88

Joined Feb 8, 2023
117
Yes, I had a 'stop being zero' resistor with my 4060 version but forgot it here. Excellent advice on this site!
Would it matter if the timer capacitor C2 was electrolytic or would a ceramic be more stable?

My pulse relay circuit.png
 
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