Need to convert a constant output voltage to single pulse, and then again with reverse polarity.

Thread Starter

Nealieboyee

Joined May 24, 2017
44
Hi All,
I have one of those cheap 7 day programmable on/off timers that turns on a relay during the ON period. What I want is to remove the relay circuit and convert the constant output voltage to a single pulse output to switch a solenoid one way. When the timer output goes to 0 during the OFF cycle, I need the single output pulse to have reverse polarity to switch the solenoid the other way. The reason for this is we are running on batteries and only want current draw during switching. The idea is the get a few months out of the batteries.

And yes, that is how this solenoid operates. One pulse will switch it on, and one pulse with reversed polarity will switch it off.

Any recommendations for a transistor or logic circuit that could achieve this?
Thanks
 

DickCappels

Joined Aug 21, 2008
8,000
I suggest using MOSFETs so you don't spend battery capacity on base drive current.

What voltage are you working with? How long of a pulse do you want are we talking about one second? Are you handy with any microcontrollers?
 

Thread Starter

Nealieboyee

Joined May 24, 2017
44
Power is 12V, but the timer produces an output of 1.25V which is then fed to a transistor to switch the 12V relay. I can do away with all of that and use the 1.25V if I want.
A pulse of 0.5-1 second would be fine. Not great with microcontrollers as I haven't had much experience with them. I'm trying to keep current draw to a minimum, so the less I introduce into the circuit, the better.
 

Thread Starter

Nealieboyee

Joined May 24, 2017
44
We need to know the operating characteristics of the solenoid. Do you have a part number or data sheet?
No part number unfortunately. But I can confirm it only needs a short (less than one second) 6V pulse to switch it one way. Then a short pulse of opposite polarity would switch it the other way.

I had a thought. What about taking the high signal from the timer and running it through two CMOS monostables? The first monostable will provide a high pulse when input is high. When input is low, the second monostable would provide a high pulse. I could then feed those two signals into either side of an H-Bridge to power the solenoid. I'll try to draw up a basic sketch of what I mean.
 

crutschow

Joined Mar 14, 2008
28,227
It's not clear what you have.

How does the timer generate 1.25V?
Does the relay generate the reverse polarity signal for the solenoid?

You mention 12V for the relay and 6V for the solenoid.
How many supply voltages do you have?

A schematic of your present circuit would be very helpful in reducing the confusion.
 

eetech00

Joined Jun 8, 2013
2,660
No part number unfortunately. But I can confirm it only needs a short (less than one second) 6V pulse to switch it one way. Then a short pulse of opposite polarity would switch it the other way.

I had a thought. What about taking the high signal from the timer and running it through two CMOS monostables? The first monostable will provide a high pulse when input is high. When input is low, the second monostable would provide a high pulse. I could then feed those two signals into either side of an H-Bridge to power the solenoid. I'll try to draw up a basic sketch of what I mean.
Measure the DC resistance of the selenoid coil. Also measure by reversing the meter leads.
Report back...

Confirm it is a single coil latching selenoid.
Confirm you want momentary input control (is the control input a button?).
 
Last edited:

eetech00

Joined Jun 8, 2013
2,660
Hi All,
I have one of those cheap 7 day programmable on/off timers that turns on a relay during the ON period. What I want is to remove the relay circuit and convert the constant output voltage to a single pulse output to switch a solenoid one way. When the timer output goes to 0 during the OFF cycle, I need the single output pulse to have reverse polarity to switch the solenoid the other way. The reason for this is we are running on batteries and only want current draw during switching. The idea is the get a few months out of the batteries.
So....you still want to use the timer output to control a latch relay?

And yes, that is how this solenoid operates. One pulse will switch it on, and one pulse with reversed polarity will switch it off.
Most latching relays work that way.
 

Thread Starter

Nealieboyee

Joined May 24, 2017
44
It's not clear what you have.

How does the timer generate 1.25V?
Does the relay generate the reverse polarity signal for the solenoid?

You mention 12V for the relay and 6V for the solenoid.
How many supply voltages do you have?

A schematic of your present circuit would be very helpful in reducing the confusion.
The timer itself has a 1.2V rechargeable battery onboard which is recharged through a zener diode when you apply the 12V supply. I believe I can get it to work off 6V instead. That way my solenoid and timer can both use the same supply.

So....you still want to use the timer output to control a latch relay?
Correct. Strip away the relay etc from the timer board and use the 1.2V timer output to control a latch solenoid.
Look for a low idle current H-bridge motor driver.
Unfortunately, low max voltage (under 10V) comes with the low idle current.

L9110 idle current is 2μA max and Vcc is 12V max.

https://www.elecrow.com/download/datasheet-l9110.pdf
Under 10V wouldn't be a problem. I'm planning to use 6V.


Attached image is what I'm hoping would work.
Timer output to two nor gate monostables. One handles the high output from the timer and and converts it to a single pulse, which goes to the H-bridge.
The low output from the timer gets inverted, sent through the second monostable and the high output pulse goes to the second input on the H-bridge.

Does this make sense?

1624635952223.jpg
 

Ian0

Joined Aug 7, 2020
3,785
Yes - it does exactly the same as my circuit in post #10
Thanks Ian. I thought yours was just a standard H Bridge driver. I see you only have one input on your schematic, though. What kind of input are you giving it?
[/QUOTE]
The pin 3 input comes from the switch. The pin 2 input is the same thing delayed by the time for which the solenoid should be energised.
So: timer output goes high, pin 3 goes high, one side of the bridge goes high, solenoid receives a positive-going pulse. After the RC Delay, the other side also goes high so the pulse ends.
When the switch goes low, everything reverses and the solenoid gets a negative going pulse.
 

eetech00

Joined Jun 8, 2013
2,660
The timer itself has a 1.2V rechargeable battery onboard which is recharged through a zener diode when you apply the 12V supply. I believe I can get it to work off 6V instead. That way my solenoid and timer can both use the same supply.
You mention "we are running on batteries". What is running on batteries? Just the timer?

But, then you are retaining the 12v supply, and the timer already runs using the 12v supply, right?
Then why change the relay drive voltage to 6V?

1.25v at less than 1ma is still enough to trigger a BJT...

obviously....I'm confused with your request..
 

Thread Starter

Nealieboyee

Joined May 24, 2017
44
Thanks Ian. I thought yours was just a standard H Bridge driver. I see you only have one input on your schematic, though. What kind of input are you giving it?
The pin 3 input comes from the switch. The pin 2 input is the same thing delayed by the time for which the solenoid should be energised.
So: timer output goes high, pin 3 goes high, one side of the bridge goes high, solenoid receives a positive-going pulse. After the RC Delay, the other side also goes high so the pulse ends.
When the switch goes low, everything reverses and the solenoid gets a negative going pulse.
[/QUOTE]
Ah that's genius. I can drop the logic gates and inverter then. Having trouble finding them in the UK though. I'll keep searching.
Thanks a lot!


Thanks for that! Looks like its available here too.


You mention "we are running on batteries". What is running on batteries? Just the timer?

But, then you are retaining the 12v supply, and the timer already runs using the 12v supply, right?
Then why change the relay drive voltage to 6V?

1.25v at less than 1ma is still enough to trigger a BJT...

obviously....I'm confused with your request..
Haha. Sorry if I've confused you.
Basically the off-the-shelf timer is designed to run from a 12V supply but we want to use batteries instead, specifically 6V worth of batteries, as the solenoid we want to switch runs from 6V.

It has two boards inside it. One contains the lcd and programmed chip. The second board just has a rectifier, some smoothing caps, Led and a transistor, as well as a 1.2V rechargeable battery and a 12V relay. Basically it collects the output from the chip and uses a transistor to switch on the relay. The rest of that board is just a basic charging circuit to keep the 1.2V cell charged.

The 1.2V cell powers the lcd and programmed chip, essentially the heart of the timer. So I need to keep that. But I don't need the relay or rectifier etc.


Now, our solenoid is a 6V solenoid. So If I can run the timer from 6V (think 4x AA cells) and ditch the relay etc. then I can modify the timer constant output to a single pulse and run our solenoid.

Hope this makes sense.
 

eetech00

Joined Jun 8, 2013
2,660
Haha. Sorry if I've confused you.
Basically the off-the-shelf timer is designed to run from a 12V supply but we want to use batteries instead, specifically 6V worth of batteries, as the solenoid we want to switch runs from 6V.

It has two boards inside it. One contains the lcd and programmed chip. The second board just has a rectifier, some smoothing caps, Led and a transistor, as well as a 1.2V rechargeable battery and a 12V relay. Basically it collects the output from the chip and uses a transistor to switch on the relay. The rest of that board is just a basic charging circuit to keep the 1.2V cell charged.

The 1.2V cell powers the lcd and programmed chip, essentially the heart of the timer. So I need to keep that. But I don't need the relay or rectifier etc.


Now, our solenoid is a 6V solenoid. So If I can run the timer from 6V (think 4x AA cells) and ditch the relay etc. then I can modify the timer constant output to a single pulse and run our solenoid.

Hope this makes sense.
Ok.
There hasn't been any "precision" timing requirements stated.
why not use a standard Transistor driver?
Current draw would be about 1ma or less while the timer output is high. If using 2200mah batteries, and the output is high 50% of the time, they’ll last about 200 days. Is that acceptable?
 
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Thread Starter

Nealieboyee

Joined May 24, 2017
44
Ok.
There hasn't been any "precision" timing requirements stated.
why not use a standard Transistor driver?
Current draw would be about 1ma or less while the timer output is high. If using 2200mah batteries, and the output is high 50% of the time, they’ll last about 200 days. Is that acceptable?
By transistor driver, you mean a transistor H-Bridge? Yeah that was going to be my first choice. I just assumed the IC versions were more economical on power.
200 days would be absoluty fine. The aim was around 3 months or more.
 
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