1 sec alternating polarity circuit

[wombweller]

Hello all.
Please see the attached photo of a circuit I’d like to copy. I don’t have the actual board a friend of mine sent me the photo.

It’s a circuit to produce 1 second alternating pulse using the following IC’s-
CD4017B x2, CD4060B x1 and a CD4024B.

Can anyone point me to a circuit diagram for this, maybe there is something online, if there is I’m unable to find it.

I think this circuit is used so it can run on 3v so low power. It’s for pulsing a low voltage Brillie slave clock and needs to be a small footprint so it can go in to the back of the clock and run on batteries.

I look forward to hearing from you.

Regards
Mark

 

[wombweller]

It would help to know what the capacitor rating is.

I will ask the owner. Thanks

 

[Diver300]

I have added the pin functions to the diagram.
I think that it is running once per minute. The output of the CD4024 that is being used is Q6 which divides by 64, so the first CD4017 is clocked at 0.5 Hz. The two CD4017s divide by 5 and 6 so the whole thing is 1/60 Hz, or once a minute.

I have labelled the transistors. Q1 is turned on for 10 seconds every minute, and the current to the clock will be a short pulse which finishes when the big capacitor charges up.

I have shown the Q2 as an NPN transistor, the same as Q1. Q2 is not a PNP transistor. If it were, it would be turned on when Q1 is turned on, so the supply would be shorted.

I think that Q2 is being used in an unconventional way, either by mistake or in a quite subtle way. It is being used as an emitter-follower, but the emitter and collector swapped. As long as the base-emitter junction does not break down, which it shouldn't at less than 6 V, Q2 will work as a transistor but with a very poor gain.

The base of Q2 is taken high for 10 seconds every minute, 30 seconds after Q1 was turned on. The purpose of Q2 is to discharge the big capacitor ready for the next pulse.

If Q2 turned on and provided a low impedance path, the capacitor would discharge just as fast as it charged, which could have an effect on the clock. By swapping collector and emitter, the gain of Q2 will be far less, maybe less than 10, so the discharging of the capacitor will be at a low current which will mean that the solenoid in the clock does nothing during the discharge.

 

[augustinetez]

Diver 300 beat me to it, although according to my datasheet Q6 is divide by 32 - going back to double check that.

 

[Diver300]

Diver 300 beat me to it, although according to my datasheet Q6 is divide by 32 - going back to double check that.

I think it is divide by 64
Q1 divides by 2
Q2 divides by 4
Q3 divides by 8
Q4 divides by 16
Q5 divides by 32
Q6 divides by 64

 

[augustinetez]

Yes, reckon you're right, I was not reading the table in the Renesas dataheet correctly.

 

[wombweller]

Yes, reckon you're right, I was not reading the table in the Renesas dataheet correctly.

I’ve sent a message to the owner to see if he can wire it up to check the output but it’s odd because he’d had it sold to him for 30seconds outputs not 60
He’s still yet to get back to me about the cap value.
Many thanks thus far, you have all provided lots of useful information.

 

[wombweller]

Hi all.
The owner has supplied the following information on the cap.
348BC0848BC084, 21 Ko021KO 021

I’ve written it has he did but it looks like a 21kO Axial.
The nearest one I can find is on eBay.

https://www.ebay.co.uk/itm/275505626411

Many thanks

 

[AnalogKid]

Hi there, the ones in question are 1sec alternating polarity

Late to the party. Please explain, maybe with a hand-drawn sketch, what this means.

Pulse amplitude(s) - ?
Pulse width(s) - ?
Peak or nominal output current - ?
Other - ?

ak

 

[AnalogKid]

By swapping collector and emitter, the gain of Q2 will be far less, maybe less than 10, so the discharging of the capacitor will be at a low current which will mean that the solenoid in the clock does nothing during the discharge.

Disagree. You show Q2 as an emitter follower. As such, the *current* gain of the pull-up circuit is the max value on the datasheet. The peak output voltage will be lower than with a saturated switch, but the output current will not be limited by the emitter-follower configuration. The output current will be whatever the load draws.

BTW since Q2 is an emitter follower, its base current limiting resistor can be deleted.

ak

 

[Nigel Goodwin]

Hi all.
The owner has supplied the following information on the cap.
348BC0848BC084, 21 Ko021KO 021

I’ve written it has he did but it looks like a 21kO Axial.
The nearest one I can find is on eBay.

https://www.ebay.co.uk/itm/275505626411

Many thanks

Bit strange he didn't bother writing the actual value down?

 

[AnalogKid]

Here is a first pass at a re-work of the #22 schematic. I did not verify that this is a correct schematic for the board in Post #1. Click on the schematic for a larger image.

Note: Adjust R1, R2, C1 and C2 for the crystal being used.

ak

 

[AnalogKid]

Hi there, the ones in question are 1sec alternating polarity

If the schematics in #16 and #22 are correct, this circuit pulses the clocks once per minute.

ak

 

[AnalogKid]

deleted

 

[wombweller]

Late to the party. Please explain, maybe with a hand-drawn sketch, what this means.

Pulse amplitude(s) - ?
Pulse width(s) - ?
Peak or nominal output current - ?
Other - ?

ak

Hi There. You can ignore that. I was initially told that the circuit outputted a 1second pulse, this was incorrect. My friend was sold the circuit and was told it outputs a pulse every 30seconds for his slave clock which requires a pulse every 30 seconds.
At this moment it is suggested that the circuit will actually be putting a pulse out every 60 seconds.
Hope this helps.

 

[wombweller]

deleted

I’ve asked my friend to check the actual circuit running to see if it is actually putting out a 1min pulse. If this is correct then he’s been sold something he can’t use .
I can make him a circuit he requires.

 

[wombweller]

To add, he was also told that it was an alternating polarity output.

 

[wombweller]

To add. I’m now told that the other transistor has this info on it-
003MAL, I’m not familiar with this one.

 

[AnalogKid]

If the requirement is one pulse (or pulse sequence) every 30 seconds, you can do that with this circuit by eliminating the CD4024.

1. Connect U1 Q14 output (pin 3) directly to the U3 clock input.

2. U3 - Delete the connection between pins 1 and 15.

Schematic on request.

Is there a min or max output pulse width spec?

ak

 

[Diver300]

To add, he was also told that it was an alternating polarity output.

The circuit gives a pulse in one direction and 30 seconds later a pulse in the other direction, so it could be considered every 30 seconds or or each minute, depending on what the mechanical mechanism of the clock is.

 

[AnalogKid]

I did a pulse clock driver back in the 70's for a TV station, but I suspect that things have changed a bit in 50 years.

ak