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

eetech00

Joined Jun 8, 2013
3,418
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.
Here is what I had in mind.

The circuit causes a polarity change across the relay coil whenever the Timer output changes.
Max current is drawn from the supply only when a change occurs and only for a few milliseconds.
If the timer contact is held closed, aapprox 1ma (or less) will be continuously drawn by the circuit.

I used a latch relay spec from a datasheet for a 12v latch relay I had. So what you see below is actually a 12v relay operated at 6 volts (I don't know if your relay actually will operate a 6v)

Q2 and Q3 could probably be mosfets instead.

1624679744622.png

Edit: Modified Circuit to provide disconnect of ground from base of Q3
 
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Thread Starter

Nealieboyee

Joined May 24, 2017
56
Is the output a changeover relay, or just a single closed contact?
The output of what? The timer itself? I think it's straight from a chip, no contacts.
Here is what I had in mind.

The circuit causes a polarity change across the relay coil whenever the Timer output changes.
Max current is drawn from the supply only when a change occurs and only for a few milliseconds.
If the timer contact is held closed, aapprox 1ma (or less) will be continuously drawn by the circuit.

I used a latch relay spec from a datasheet for a 12v latch relay I had. So what you see below is actually a 12v relay operated at 6 volts (I don't know if your relay actually will operate a 6v)

Q2 and Q3 could probably be mosfets instead.

View attachment 242137
Ooh that's an interesting one. Thank you. I might have to build that one this weekend. And that would reverse polarity on the relay/solenoid every time the input from my time goes from 1.2v to 0v and back again?
 

eetech00

Joined Jun 8, 2013
3,418
The output of what? The timer itself? I think it's straight from a chip, no contacts.

Ooh that's an interesting one. Thank you. I might have to build that one this weekend. And that would reverse polarity on the relay/solenoid every time the input from my time goes from 1.2v to 0v and back again?
yes. You can run on a 12v supply if you want.
 

Ian0

Joined Aug 7, 2020
6,660
If you had a changeover relay a circuit as simple as this would probably work, but you might have to experiment with the capacitor value.119B5A73-5DE2-4C6A-8CEA-AF8670A0B30D.jpeg
 

eetech00

Joined Jun 8, 2013
3,418
The output of what? The timer itself? I think it's straight from a chip, no contacts.

Ooh that's an interesting one. Thank you. I might have to build that one this weekend. And that would reverse polarity on the relay/solenoid every time the input from my time goes from 1.2v to 0v and back again?
I've bread boarded the circuit, tested, and it now works.
See modified circuit post#22..
I've added Q4 to disconnect the ground from the base of Q3.
The circuit works perfectly with an input of 1.2 volts and a supply of 12v. I wasn't able to test lower than 9v because the 12v latch relay I used had a drop out voltage of 9v but the circuit should work down to 6v. However, it does use about 3.8ma when input is high. Might be able to adjust this.
 
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MrChips

Joined Oct 2, 2009
27,651
I've bread boarded the circuit and tested. Decided against it. Doesn't work as intended and requires too much power.
Removed from post #22.
When you delete a post all references to a post # go out of whack.
Also it makes readers confused about what other posts are referring to. It creates an unknown hole in the following discourse.
It would be best to leave the post and add an edit to say you tested it and it is not a recommended solution.

I have restored your posts. Go ahead and add an Edit statement.
Do not alter the original contents.
 

eetech00

Joined Jun 8, 2013
3,418
When you delete a post all references to a post # go out of whack.
Also it makes readers confused about what other posts are referring to. It creates an unknown hole in the following discourse.
It would be best to leave the post and add an edit to say you tested it and it is not a recommended solution.

I have restored your posts. Go ahead and add an Edit statement.
Do not alter the original contents.
The circuit works after all.
I've modified the circuit in post #22 and added an EDIT comment.

thanks.
 

Thread Starter

Nealieboyee

Joined May 24, 2017
56
I've bread boarded the circuit, tested, and it now works.
See modified circuit post#22..
I've added Q4 to disconnect the ground from the base of Q3.
The circuit works perfectly with an input of 1.2 volts and a supply of 12v. I wasn't able to test lower than 9v because the 12v latch relay I used had a drop out voltage of 9v but the circuit should work down to 6v. However, it does use about 3.8ma when input is high. Might be able to adjust this.
Thank you very much for this. I'll give it a test tomorrow. 3.8mA might be a bit high but it would probably only be high during evening hours, so roughly 1/3rd of the time. I'll have to calculate what that would do for battery life. Did you measure current draw during input low?
 

eetech00

Joined Jun 8, 2013
3,418
Thank you very much for this. I'll give it a test tomorrow. 3.8mA might be a bit high but it would probably only be high during evening hours, so roughly 1/3rd of the time. I'll have to calculate what that would do for battery life. Did you measure current draw during input low?
yes . Too low to measure.
 

eetech00

Joined Jun 8, 2013
3,418
Circuit in post #31 works as intended.
Current draw with 12v supply and values shown, (except M1,M2=2N7000-G, M3=ZVP4424A) is about 750uA with input at 1.2v.
With input at 0v, too low to measure.
Current draw with 9v supply and values shown, (except M1,M2=2N7000-G, M3=ZVP4424A) is about 550uA with input at 1.2v.
With input at 0v, too low to measure.
 

Thread Starter

Nealieboyee

Joined May 24, 2017
56
Circuit in post #31 works as intended.
Current draw with 12v supply and values shown, (except M1,M2=2N7000-G, M3=ZVP4424A) is about 750uA with input at 1.2v.
With input at 0v, too low to measure.
Current draw with 9v supply and values shown, (except M1,M2=2N7000-G, M3=ZVP4424A) is about 550uA with input at 1.2v.
With input at 0v, too low to measure.
That's great thank you. Amazing how much the current drops using MOSFETs.
Would there be a simple way of incorporating a photocell into it so that it doesn't turn on during daylight hours? The timer takes care of preprogrammed hours, but in summer it's still light until almost 10pm. Any photocell would do.
 

eetech00

Joined Jun 8, 2013
3,418
That's great thank you. Amazing how much the current drops using MOSFETs.
Would there be a simple way of incorporating a photocell into it so that it doesn't turn on during daylight hours? The timer takes care of preprogrammed hours, but in summer it's still light until almost 10pm. Any photocell would do.
So you want the photocell to replace the timer? Or?
 

Thread Starter

Nealieboyee

Joined May 24, 2017
56
So you want the photocell to replace the timer? Or?
No the timer will always work and provide input to your circuit, but the photocell needs to stop the solenoid being switched on if it is still light outside. Imagine if your photocell was the switch SW. If it sees light, then the switch would be open, stopping the base of Q1 from ever going high. Problem is, if a shadow from a cloud passes over the photocell, it would turn on the solenoid. If there was a waiting option so it only turns on if it has been dark for a few minutes. Does that make sense?
 

eetech00

Joined Jun 8, 2013
3,418
No the timer will always work and provide input to your circuit, but the photocell needs to stop the solenoid being switched on if it is still light outside. Imagine if your photocell was the switch SW. If it sees light, then the switch would be open, stopping the base of Q1 from ever going high. Problem is, if a shadow from a cloud passes over the photocell, it would turn on the solenoid. If there was a waiting option so it only turns on if it has been dark for a few minutes.
Does that make sense?
No. Not to me. :DA cloud would have to lower the ambient light level to the same level as "Dark". :confused: So seems unnecessary. The threshold for the photocell would be adjustable.

However, an (IC) timer could be added to the photocell circuit to "enable" the relay circuit. It raises complexity but can be done (I was trying to avoid using chips).

But why wouldn't you just reset your timer for a longer OFF time.
 

Thread Starter

Nealieboyee

Joined May 24, 2017
56
No. Not to me. :DA cloud would have to lower the ambient light level to the same level as "Dark". :confused: So seems unnecessary. The threshold for the photocell would be adjustable.

However, an (IC) timer could be added to the photocell circuit to "enable" the relay circuit. It raises complexity but can be done (I was trying to avoid using chips).

But why wouldn't you just reset your timer for a longer OFF time.
Ah yes you're right. Darkness would make it a lot darker than a passing cloud would. What about a light dependent resistor in a mosfet switch? It could use a variable resistor to set the light threshold. The mosfet would switch the line where SW is in your circuit? I'm really rusty with this stuff.
 

eetech00

Joined Jun 8, 2013
3,418
Ah yes you're right. Darkness would make it a lot darker than a passing cloud would. What about a light dependent resistor in a mosfet switch? It could use a variable resistor to set the light threshold. The mosfet would switch the line where SW is in your circuit? I'm really rusty with this stuff.
actually, an LDR is what I was going to use along with a TLV431 configured as a comparator. The TLV431 would drive the existing BJT. The timer output and the LDR circuit would be ANDed together.

Are you sure your latch relay will operate at 6v?
Can you take a photo of the relay to show part number?
 
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Thread Starter

Nealieboyee

Joined May 24, 2017
56
actually, an LDR is what I was going to use along with a TLV431 configured as a comparator. The TLV431 would drive the existing BJT. The timer output and the LDR circuit would be ANDed together.

Are you sure your latch relay will operate at 6v?
Can you take a photo of the relay to show part number?
How would you AND the timer output and LDR together? Just using the TLV431 or would you need to use a logic IC?
The solenoid is definitely 6VDC. It's written on it and I can actuate it with 4x AAA cells.
 

eetech00

Joined Jun 8, 2013
3,418
How would you AND the timer output and LDR together? Just using the TLV431 or would you need to use a logic IC?
Don't need an IC (yet). I'll use an additional mosfet.
The solenoid is definitely 6VDC. It's written on it and I can actuate it with 4x AAA cells.
Ok.

Does the timer output go high at night and low during day? Or does it matter to you?
 
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