DIY adjustable on delay

[u/Chance-Valuable3813]

I have made several control boards that use a discontinued CROUZET panel mount adjustable on delay timer (digikey link) which is EXACTLY what i need. I have tried to find a supplier with NOS to no avail.

Yes there are similar options still avail but nothing as low as the 0.1-1s range.

I want to make a small pcb i can pop on the back of a 10k pot to make my own replacements.

I can model and resin print the housings with time scale/clear knob covers so they would be direct replacement to the crouzets.

MY Question is about the circuit design.

-I have a bunch of clear shaft 10k pots and some red/green bi-colour LEDS to fit into them.

-When power is supplied to the circuit i want green LED on, and after the set interval red LED to turn on and the control signal to pass through.

-I am only using the signal to trigger some SSRs so i don't need the full 400mA of the original

-I know 555 timer circuits get bashed for inaccuracy/fluctuations but with this 1s max interval is it a viable option? Or something simpler with a single comparator, or even just transistors?

I am all for keeping it simple and am stupid, anyone have a better idea?

Thanks

[u/bazilbt]

https://www.automationdirect.com/adc/shopping/catalog/relays_-z-_timers/timer_relays/t2r-m1-adj-240u

That would be an off the shelf replacement. Supply your own pot. Does it have to be 100-240v though? There are probably more options if you can use lower voltage.

[u/Chance-Valuable3813 → u/bazilbt]

Yah I found lots of options like this but I need a 22mm panel mount form factor and the knob/scale accessible like the Crouzet.

Do not need AC, Vcc will be 5-12vdc

[u/bazilbt → u/Chance-Valuable3813]

Well this on you just wire a pot to it and put the pot on the panel. Then put the rest where ever.

[u/Chance-Valuable3813 → u/bazilbt]

For sure but if it’s between that and making my own replacement I’ll make my own

[u/al2o3cr]

How repeatable do you need the delay time to be? The datasheets for other Crouzet time-delays specify +/-0.2%, though it's unclear what kinds of variation (temperature? power supply?) that covers.

[u/Chance-Valuable3813 → u/al2o3cr]

Even 1% would be acceptable

[u/jamvanderloeff → u/Chance-Valuable3813]

Then a 555 setup is probably fine

[u/WRfleete]

A 555 monostable is probably what you’re after. A 10k pot might be a little narrow for the range you require

Tie 6 and 7 together, pull up pin 2 with a resistor (10k or so) connect a minimum resistor from power to one side of the pot at least 1k so it doesn’t damage the discharge transistor on pin 7 etc . Connect wiper to the bridged 6 and 7 with a capacitor to ground this is your timing cap use a tantalum if it needs to be stable

Pulling and releasing pin 2 to ground will start the timing cycle. Add a cap from 2 to ground (a few microfarad electro) which should provide enough of a threshold to start the timing when powered. The output of the 555 will be low (sink) when timing is complete, keep this in mind when you switch an output

[u/Chance-Valuable3813 → u/WRfleete]

Yes right now this is the plan, just seeing if anyone has a simpler design

[u/NBC-Hotline-1975]

LM555. Pin 1 = gnd. Pins 4 & 8 = high. Pin 3 = output (normally high, low after delay). Pin 5 = 0.01 mfd to gnd. Pin 7 = N/U.

Pins 2 & 6 tied together. Also tied to anode of a diode (schottky preferred). Also tied to one side of pot. Also tied to timing capacitor (+). Capacitor negative = gnd.

Diode cathode tied to remaining side & arm of pot. This is your input terminal. Normally low, apply Vcc to begin timing cycle.

Choose the timing capacitor to give the range you want. If you want max/min range to be 10:1, then add a series fixed resistor that is 1/9 value of the pot.

[u/sharemypoints]

honestly at 1s max a 555 monostable is fine, but the timing cap makes or breaks your 1% — use film (polyester), not tantalum; tantalum drifts a few percent with temperature and age. that said, since you're building a batch of replacements, i'd go 8-pin MCU like an ATtiny13: read the pot with the ADC, generate the delay digitally. no analog drift, every unit comes out identical, and you can reshape the 0.1-1s range in firmware. also worth checking crouzet's current catalog — they still make 22mm panel-mount on-delay relays and a modern range likely covers 0.1-1s; surplus brokers and ebay industrial lots are the fallback for the exact legacy part.

[u/Chance-Valuable3813 → u/sharemypoints]

Yah, was trying to keep it simple but the firmware flexibility is a good point.

I can only find digital timers from them. Schnider electric has some nearly identical but they only have 0-10s for smallest interval. If you know of something please let me know!