Ground triggered Latching Circuit using transistors

hp1729

Joined Nov 23, 2015
2,304
I have combined your diagram with the Flip Flop I posted earlier and attached it to this post. Is this what you had in mind?

So increase the resistor value to the LED from 330 to 1K. Correct? If so, I didn't show that on the drawing.

Are you thinking I need resistor to 12v after the N.O. push button in my drawing?

Thank you for all the input here guys.

TONY

cmartinez

Joined Jan 17, 2007
8,285
I have combined your diagram with the Flip Flop I posted earlier and attached it to this post. Is this what you had in mind?

So increase the resistor value to the LED from 330 to 1K. Correct? If so, I didn't show that on the drawing.

Are you thinking I need resistor to 12v after the N.O. push button in my drawing?

Thank you for all the input here guys.

TONY
My only observation would be that R9's value seems too high to drive the base of Q1. Probably a 1K to 2K resistor would be better for that purpose.

dl324

Joined Mar 30, 2015
17,125
They're 100pF, 100 microfarads would be 100uF. The cap values aren't critical; it depends on the maximum toggle rate of the flip flop.

dl324

Joined Mar 30, 2015
17,125
My only observation would be that R9's value seems too high to drive the base of Q1. Probably a 1K to 2K resistor would be better for that purpose.
You're right. I used 200 in my example to give 2X the base current required to insure the transistor saturated. The current in Q1 will be around 300mA, so the base current should be at least 30mA; 200 ohms will give around twice that.

stillgrowingup

Joined Jul 15, 2015
210
You're right. I used 200 in my example to give 2X the base current required to insure the transistor saturated. The current in Q1 will be around 300mA, so the base current should be at least 30mA; 200 ohms will give around twice that.
So R9 should be 200 ohms, NOT 220k?

TONY

dl324

Joined Mar 30, 2015
17,125
So R9 should be 200 ohms, NOT 220k?
Yes. You could try 220K to convince yourself that it won't provide enough base current to saturate the transistor...

cmartinez

Joined Jan 17, 2007
8,285
Yes. You could try 220K to convince yourself that it won't provide enough base current to saturate the transistor...
And that's the beauty of breadboarding a circuit before making a pcb... it not only allows you to more easily correct mistakes, but also to experiment with endless "what if" scenarios as well. And have a far fuller learning experience in the process.

stillgrowingup

Joined Jul 15, 2015
210
Thank you guys. I have came up with a different drawing, hoping for the same result. The second drawing has less components. Please look them over and offer feedback. Ultimate goal is to have a working circuit that is durable. This circuit will be active for 6 hours per day. Not to mention the heat of sitting car in sunlight during the summer months.

TONY

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Alec_t

Joined Sep 17, 2013
14,408
The first circuit won't toggle reliably if there is no pull-up resistor from C1/C2 to the 12V rail.
The second circuit should latch, but I don't see how it will toggle?

dl324

Joined Mar 30, 2015
17,125
Agree; don't see how the second circuit can toggle.

stillgrowingup

Joined Jul 15, 2015
210
The first circuit won't toggle reliably if there is no pull-up resistor from C1/C2 to the 12V rail.
The second circuit should latch, but I don't see how it will toggle?
I added a 10k resistor for a Pull-up. Hopefully in the right spot. ... Not sure if 10k will be the right value, but it's a start. I added the updated drawing to this post.

Agree; don't see how the second circuit can toggle.
And I was hoping I understood this when I drew it up. .. is the 2nd drawing hopeless?

TONY

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cmartinez

Joined Jan 17, 2007
8,285
I added a 10k resistor for a Pull-up. Hopefully in the right spot. ... Not sure if 10k will be the right value, but it's a start. I added the updated drawing to this post.

And I was hoping I understood this when I drew it up. .. is the 2nd drawing hopeless?

TONY
Yup, you placed the resistor in the right place. And 10k should be more than enough to bias the node.

stillgrowingup

Joined Jul 15, 2015
210
@stillgrowingup, I suggest you take a look at Mr Chip's blog regarding flip-flop fundamentals. It's quite illustrative.
Thank you. I did find it helpful.

Hello guys,

I have downloaded MulitSim 13 and found it easy to use for a beginner like me.
Trying everything I can think of, incorporating some recommendations I you all have given. Thank you. I think I have the solution. Using a 4013 IC. Output to handle External Lamp, Relay and LED. Being triggered from a Ground source N.O. push button.

I do have some questions. From what I can tell, this chip can do this same circuit twice, but independently? Is this Correct? I hope so, I need 2 toggle latching circuits.

Can I use a 1N4004 diode across the relay coil instead of a 1N4148? Not sure what the difference is.

C3 is for filtering Automotive noise, figured I needed it.

How do my Cap values look? It does work well in the simulator. But funny thing ... When I try to put the voltmeter on the output of the BD139. It latches on, without releasing. ... Also when I place the Voltmeter across the C1 to measure the cap voltage. It latches on, without releasing. Not sure why.

Thanks
TONY

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dl324

Joined Mar 30, 2015
17,125
From what I can tell, this chip can do this same circuit twice, but independently? Is this Correct? I hope so, I need 2 toggle latching circuits.
Yes. If you had decided to go with the IC sooner, you could have saved everyone some effort...
Can I use a 1N4004 diode across the relay coil instead of a 1N4148? Not sure what the difference is.
Yes. The important thing is that the diode be able to handle the relay coil current.
C3 is for filtering Automotive noise, figured I needed it.
Make sure you put it across the power pins of the flip flop. You may need more (i.e. an electrolytic) because auto electrical can be very noisy.
How do my Cap values look?
What is C1 for and why is it so large? If it's for switch debouncing, I'd put it across the switch. I'd also change R1+R2 to be something like 10K.

What is the function of C2 and R4? They seem unnecessary to me.

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cmartinez

Joined Jan 17, 2007
8,285
Can I use a 1N4004 diode across the relay coil instead of a 1N4148? Not sure what the difference is.
Yes you can, their main difference is their current carrying capability, in which the 1N4004 may be a better choice.

C3 is for filtering Automotive noise, figured I needed it.
Make sure you place is as close to yout 4013 chip as possible

How do my Cap values look? It does work well in the simulator. But funny thing ... When I try to put the voltmeter on the output of the BD139. It latches on, without releasing. ... Also when I place the Voltmeter across the C1 to measure the cap voltage. It latches on, without releasing. Not sure why.
C1 is HUGE! you could probably use a much smaller value, if you increase R1 a bit more. Try to bring it down to 100uF or less, if you can. Use the simulator to find out the best value for R1

stillgrowingup

Joined Jul 15, 2015
210
Thank you guys.

Yes. The important thing is that the diode be able to handle the relay coil current.
I have plenty of 1N4004. I'll use those.

Make sure you put it across the power pins of the flip flop.
Make sure you place is as close to yout 4013 chip as possible

Do you mean put C3 right at the pin 14 (Vdd)? Or put the C3 to Pin 7 (Gnd) and pin 14 (Vdd)? .. I also put electrolytic caps in.

What is C1 for and why is it so large? If it's for switch debouncing, I'd put it across the switch.
Yes it was. It wasn't til I increased the C1 that the switch was steadily toggling. I decreased C1 and changed R1 and R2 values, per your recommendations. Things seem to toggle nicely in the SIM now.

What is the function of C2 and R4? They seem unnecessary to me.
I saw this in someone else's circuit. I tried putting them to ground in this SIM. It still worked. I'll see what happens on a breadboard.

In the SIM, circuit becomes active at start up. I do NOT want that. So I first swapped Pin 1 and 2. Then the circuit won't toggle in the SIM. So I next removed the ground from pin 4 (RESET input). Added a the cap to go from pin 4 to +12v. Then 10k resistor needs to go from pin 4 to ground. Hoping the cap will pull the RESET input high by following the 12v supply when first powered on, and then the resistor will charge the capacitor, pulling the RESET input back to ground.

Still the circuit became active on SIM power up. I then increase the resistor to 47k or 100k. Still became active on SIM startup. I next added the other half of the chip to the SIM and grounded pins 10, 9 and 8 I think I need to do breadboard SIM and see what happens.

TONY

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dl324

Joined Mar 30, 2015
17,125
I saw this in someone else's circuit. I tried putting them to ground in this SIM. It still worked. I'll see what happens on a breadboard.
I don't think they serve any useful purpose and should be removed; lest more people ask you why they're there and you not having a good reason.
In the SIM, circuit becomes active at start up. I do NOT want that. So I first swapped Pin 1 and 2. Then the circuit won't toggle in the SIM. So I next removed the ground from pin 4 (RESET input). Added a the cap to go from pin 4 to +12v. Then 10k resistor needs to go from pin 4 to ground. Hoping the cap will pull the RESET input high by following the 12v supply when first powered on, and then the resistor will charge the capacitor, pulling the RESET input back to ground.
R6 and C4 should reset at power on.

You should put C1 across the switch and remove the parallel resistor.

eetech00

Joined Jun 8, 2013
4,051
What's the total current draw for that incandescent bulb plus the relay and LED?
You'll need to make sure Q1 has enough base current to drive all of them.

dl324

Joined Mar 30, 2015
17,125
You'll need to make sure Q1 has enough base current to drive all of them.
Good catch. In the discrete design there was a small signal transistor to boost base drive for the power transistor. OP removed it and it's still needed. Power transistor load is about 300mA and the flip flop will only be able to provide a fraction of the required 30mA.