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Variable parallel delay circuits for Solenoids

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Photosbykev

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Hi folks,

I'm totally new to the forum but this seems to be the place to find an answer for a small project I'm developing :)

I use an electronic timing system to control a 24vDC solenoid valve which releases water droplets into a tray of water for photography. The timing system then waits for a trigger from an IR beam before starting two more timers to control the camera and flashguns. For one solenoid the system is very very consistent but moving onto 2 solenoids I have a problem.

Each solenoid valve has it's own mechanical response to a 24dDC pulse so when I parallel up two solenoids I get a small but visible variation in droplet position i.e. this type of thing On the right the second droplet has impacted the spout from the 1st droplet, on the left the 2nd droplet has only just reached the 1st droplet spout.

This response variation is typically a few milliseconds i.e less than 10 milliseconds.

My aim is to get 4 solenoid valves runnning to capture 4 droplet collisions in one photograph but each valve will need it's own variable timing delay that will delay the control pulse stream so I can dial out the mechanical variations.

The output of each timing circuit will need to switch 24vDC @ <300mA.

The control stream is typically 0v (open circuit) before I start the sequence then a 24v pulse for 9-10ms then a delay of 50-60ms @ 0v followed by another 9-10ms 24v pulse. The circuit should allow the control stream pulse to be replicated on the output side of each delay circuit but delayed by a variable amount of milliseconds

A very long winded description, which I apologise for, but hopefully someone will have an idea or ideas :)

best regards
Kev Lewis
 
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mneary

New Member
How much delay adjustment do you need? Do you want the output pulse duration to be equal to the input pulse, or can the output pulses all terminate when the input pulse terminates?

The analog solution is to make fine adjustments in the drive voltage. Try a 10 or 20 ohm potentiometer in series with the fastest solenoid and see if it slow down enough. Unfortunately this will have to be rated for 300mA or at least 1 watt. Mabe this 20 OHM 5 WATT WIRE WOUND POTENTIOMETER | AllElectronics.com would be a good thing to try.

If the adjustment is too sensitive, put a low-value resistor in parallel with the pot. For example if you find you're only using the first 1/4 (5 ohms) of the adjustment, put a 7-10 ohm 1W resistor in parallel. Here's one place to try - I see a 12 ohm 3W resistor that would be handy to have on hand if you're already ordering. All Electronics | Electronic and Electro-Mechanical Parts and Supplies at Discount Prices

oops I just noticed you are in UK. Hopefully you have an equivalent source of cheap parts.
 
Last edited:

Photosbykev

New Member
How much delay adjustment do you need? Do you want the output pulse duration to be equal to the input pulse, or can the output pulses all terminate when the input pulse terminates?

The analog solution is to make fine adjustments in the drive voltage. Try a 10 or 20 ohm potentiometer in series with the fastest solenoid and see if it slow down enough. Unfortunately this will have to be rated for 300mA or at least 1 watt. Mabe this 20 OHM 5 WATT WIRE WOUND POTENTIOMETER | AllElectronics.com would be a good thing to try.

If the adjustment is too sensitive, put a low-value resistor in parallel with the pot. For example if you find you're only using the first 1/4 (5 ohms) of the adjustment, put a 7-10 ohm 1W resistor in parallel. Here's one place to try - I see a 12 ohm 3W resistor that would be handy to have on hand if you're already ordering. All Electronics | Electronic and Electro-Mechanical Parts and Supplies at Discount Prices

oops I just noticed you are in UK. Hopefully you have an equivalent source of cheap parts.

Thank you for your response :)

How much delay adjustment do you need?

Each solenoid will have its own unique delay value but typically it will be a few milliseconds. If I had 20ms delay adjustment that would cover everything.


Do you want the output pulse duration to be equal to the input pulse, or can the output pulses all terminate when the input pulse terminates?

The output pulse durations have to accurately match the the input pulse durations as the length of the pulse defines the opening time of the valve.

I'm not electronic but I can solder like a pro :) I have a feeling the analogue answer might be too sensitive to accurately control with all the variables that could affect it, things like coil temperature etc.

This image clearly shows the problem
, the right hand droplet hasn't hit the water yet and the 2nd droplet isn't yet in the picture

Is there such a thing as an adjustable delay buffer circuit? i.e feed a signal into it and then a few milliseconds later the signal pops out the other end.

regards
Kev
 
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