Can't leave well enough alone

Thread Starter

Chipper

Joined Jul 19, 2018
55
About 1 year ago, I posted about trying to find a way to control high current latching relays in my 200 amp hour lithium battery powered camper I was building. Thanks to forum members, I was able to build a NE555 circuit that latched the charging circuit off when directed by the Orion jr BMS...works fine and is still doing the job.
But here goes. . . Now I want to take it to the next level. The BMS controls both charge and discharge by pulling to ground up to 175ma to enable and releases to enable/disable charge and discharge. I would like to tap into front edge trigger to provide one shot to the two coil latching relay to latch on the relay (enable charge), and then to use the rear edge trigger to one shot the other coil to latch off the relay. The time between the edge pulses could be a few minutes or even days. That depends on charge available from solar panels, alternator, etc. To me it looks like a job for a pair of 555's or a 556 IC. I suspect someone has done this before but I've looked all day and haven't found it. As always, any help would be greatly appreciated.
 

Thread Starter

Chipper

Joined Jul 19, 2018
55
... not entirely comprehending the problem, but there are edge detecting flip-flop logic devices. ... Probably a little more to it though.
edge detecting devices
Thanks for the input. I read the attached articles and yes there does appear to be a solution there. What circuits or devices are available that you might be able to point me to?
 

Thread Starter

Chipper

Joined Jul 19, 2018
55
Thanks. I’ve been doing some more reading and it looks like I’ve got some even more to do. Good night I’ll post some thoughts tomorrow
 

crutschow

Joined Mar 14, 2008
25,263
I would like to tap into front edge trigger to provide one shot to the two coil latching relay to latch on the relay (enable charge), and then to use the rear edge trigger to one shot the other coil to latch off the relay.
What is the signal voltage level, the relay coil voltage rating, and the power supply voltage?
 

crutschow

Joined Mar 14, 2008
25,263
I would like to tap into front edge trigger to provide one shot to the two coil latching relay to latch on the relay (enable charge), and then to use the rear edge trigger to one shot the other coil to latch off the relay
How about using a 555 one-shot triggered from the trailing edge to reset the relay, and a 555 one-shot with a CD4049 inverter at its input to trigger from the leading edge and set (latch) the relay, like below?

1576044261333.png
 

Thread Starter

Chipper

Joined Jul 19, 2018
55
How about using a 555 one-shot triggered from the trailing edge to reset the relay, and a 555 one-shot with a CD4049 inverter at its input to trigger from the leading edge and set (latch) the relay, like below?

View attachment 194278
Thanks crutschow, I very much like this solution. clean and cheap. I wonder what will happen on power up and power down? I'll wait for reply at 1:36 AM ;)
 

crutschow

Joined Mar 14, 2008
25,263
I wonder what will happen on power up and power down?
The simulation is ambiguous on that.
One 555 model I have shows it will output a pulse upon power-up and the other model doesn't.

If it's important that there be no pulse on power up or down, than some sort of power-up interlock circuit may have to be added.
 

Thread Starter

Chipper

Joined Jul 19, 2018
55
The simulation is ambiguous on that.
One 555 model I have shows it will output a pulse upon power-up and the other model doesn't.

If it's important that there be no pulse on power up or down, than some sort of power-up interlock circuit may have to be added.
I'll have to think about that one.. your part number CD4049B? can it be replaced with CD4049UBE?
 
What you would require to do, is to have a circuit which will hold the reset pin 4 low, during power up or power down.

That will prevent the 555 from responding to spurious pulses.
 

Thread Starter

Chipper

Joined Jul 19, 2018
55
What you would require to do, is to have a circuit which will hold the reset pin 4 low, during power up or power down.

That will prevent the 555 from responding to spurious pulses.
I'm just not sure what state the charge/discharge requirements would be in on power up mode. normally everything would be in a low state of discharge and a possible solar charge input. my hopes are to get this system to a near hands off situation.
 

Thread Starter

Chipper

Joined Jul 19, 2018
55
I'm just not sure what state the charge/discharge requirements would be in on power up mode. normally everything would be in a low state of discharge and a possible solar charge input. my hopes are to get this system to a near hands off situation.
next step is to get the inverter chip and mock this up, looks pretty simple to do. let you know next week...cj
 

Thread Starter

Chipper

Joined Jul 19, 2018
55
How about using a 555 one-shot triggered from the trailing edge to reset the relay, and a 555 one-shot with a CD4049 inverter at its input to trigger from the leading edge and set (latch) the relay, like below?

View attachment 194278
having a little trouble understanding the V2 symbol in the circuit just before the inverter. is this the same input as the input on the right hand 555 but just inverted, how can i mock this up without having a cd4049b
 

crutschow

Joined Mar 14, 2008
25,263
having a little trouble understanding the V2 symbol in the circuit just before the inverter. is this the same input as the input on the right hand 555 but just inverted,
V2 generates the trigger input.
Yes, it's inverted from the right 555 by U3.
how can i mock this up without having a cd4049b
You can with a transistor inverter.
Do you have any transistors available?

Below is the simulation with the added hold-off circuit to both Reset inputs to prevent spurious operation during power-up, as ST suggested.
I wouldn't think there would be any problem during power down, since the complete circuit is being unpowered.

1576106218425.png
 

Thread Starter

Chipper

Joined Jul 19, 2018
55
V2 generates the trigger input.
Yes, it's inverted from the right 555 by U3.

You can with a transistor inverter.
Do you have any transistors available?

Below is the simulation with the added hold-off circuit to both Reset inputs to prevent spurious operation during power-up, as ST suggested.
I wouldn't think there would be any problem during power down, since the complete circuit is being unpowered.

View attachment 194344
Do U3 and U4 represent different channels on the same chip?
 

Thread Starter

Chipper

Joined Jul 19, 2018
55
sti
V2 generates the trigger input.
Yes, it's inverted from the right 555 by U3.

You can with a transistor inverter.
Do you have any transistors available?

Below is the simulation with the added hold-off circuit to both Reset inputs to prevent spurious operation during power-up, as ST suggested.
I wouldn't think there would be any problem during power down, since the complete circuit is being unpowered.

View attachment 194344
I'm still having some trouble mocking this up... should Vin be discreet from Vdd? U1 is input from Vin through R4/c2 but and I get a pulse only when i pull it back down to 0v. am I missing something? I haven't done anything with pin4 on either chip. I'm also using NE555P (TI), will this work with the RC values given? I could also be missing something with the transistor inverter?
 
Top