hey all,
I am in need for a circuit that makes a toggle switch into a pulse switch.
Tricky sidenote. It needs to generate a pulse (pull down) on every toggle change.

So toggle on - 1 pulse
toggle off - 1 pulse

Any of you bright minds that can come up with a simple circuit that i can make in easyADA??

many thanks in advance

greetz marco

 

It can be done, but what supply voltages are available and what is the pulse load?

 

Welcome to AAC!

What is the supply voltage, desired pulse width, and what will it be driving?

 

It can be done, but what supply voltages are available and what is the pulse load?

5v and max 200mA

 

How about the pulse width?

 

How about the pulse width?

SO to clarify,
This circuit is for a DHD RM2200D faderstart. The faderstarts work with a pull down and stay active when the channel is on.
This pulse system needs to toggle a USB controller. So very little power and a pulse width of around 10ms.
i have attached a circuit from the manual

many thanks for your time

 

So very little power and a pulse width of around 10ms.

You stated it required 200mA(?).

Below is the LTspice sim of a circuit that I think does what you want:
It uses a CD4093 quad Schmitt-trigger NAND gate IC, configured as an XOR gate to generate a pulse on both the on and off of the switch.

When the switch turns on and off (green trace) it generates a pulse (yellow trace) at each transition, which turns on the M1 N-MOSFET (red trace).
The pulse width shown is about 12ms, which can be adjusted by changing the value of R1.

Edit: Added C2 and changed values of R1 and R2 to add switch-bounce suppression

 

You stated it required 200mA(?).

Below is the LTspice sim of a circuit that I think does what you want:
It uses a CD4093 IC configured as an XOR gate to generate a pulse on both the on and off of the switch.

When the switch turns on and off (green trace) it generates a pulse (yellow trace) at each transition, which turns on the M1 N-MOSFET (red trace).
The pulse width shown is about 17ms, which can be adjusted by changing the value of R1.

View attachment 302020

you are truly amazing. Time for me to get the breadboard out.
many thanks.
when i have the final result i will reply here.

 

Did this for another thread in 2017.

R3 / C3 form a switch-debounce delay of about 20 ms. If your switch causes false outputs, increase R3.

I'm not sure why R2 does not equal R1. That might be something to do with the original thread. I see that you stated an output pulse width. For approx. 10 ms, R1 = R2 = 100K, and C1 = C2 = 0.1 uF.

This circuit makes a positive-going pulse for each switch opening and closing. For a "pull-down" output, add an NPN or n-channel transistor at U1Cpin10. A 2N4401 can handle 200 mA, with a 390 ohm base resistor.

ak

 

AK's circuit reminded me that switch-bounce suppression is likely a good idea, so I added that to my circuit in post #7.

 

I am in need for a circuit that makes a toggle switch into a pulse switch.
Tricky sidenote. It needs to generate a pulse (pull down) on every toggle change.

Here's a schematic that uses an SPDT toggle switch, an electromagnetic relay and an electrolytic capacitor.



In one position of the toggle switch, the relay pulses as the capacitor charges through its coil.

In the other position the relay pulses again as the capacitor discharges through its coil.

The pulse width is determined by the time constant (relay coil resistance * capacitance).

The 'NO' contact of the relay is used for the 'pull-down'.

Nandu.

 

AK's circuit reminded me that switch-bounce suppression is likely a good idea, so I added that to my circuit in post #7.

I wondered where it was. I assumed you would just add a cap in parallel with R4.

ak

 

Thank you again.
The “ pulldown” transistor will be added.
I might use an opto isolator for that.
That way inam sure both systems wont interfere.
This is the setup!

 

I wondered where it was. I assumed you would just add a cap in parallel with R4.

For that I would need to add a small resistor in series with the switch to limit the transient charge current into the capacitor.

 

Use a SPDT switch, and connect the output terminals together. Nearly all switches of that type are break-before-make, so it will generate a positive-going pulse when neither terminal is connected.

 

I might use an opto isolator for that.

Most standard optocouplers cannot handle 200 mA. For example, a 4N35 is rated for 50 mA continuous and 100 mA pulsed. OptoFET (?) devices are more like miniature solid state relays. They use photo-activated MOSFETs, and some are rated up to 2 A.

ak

 

For that I would need to add a small resistor in series with the switch to limit the transient charge current into the capacitor.

I knew that was coming the moment I hit "post".

ak

 

Use a SPDT switch, and connect the output terminals together. Nearly all switches of that type are break-before-make, so it will generate a positive-going pulse when neither terminal is connected.

That's a simple way if the switch contact transfer time is sufficient to generate the desired pulse width.
Typically I would expect that to be only a few ms.
You could stretch that time by adding a diode and capacitor on the output.

 

Most standard optocouplers cannot handle 200 mA. For example, a 4N35 is rated for 50 mA continuous and 100 mA pulsed. OptoFET (?) devices are more like miniature solid state relays. They use photo-activated MOSFETs, and some are rated up to 2 A.

ak

The maximum allowed current in the circuit is 200mA. With your circuit i wont get near that.
the opto isolator will only switch a usb button on a gamecontroller (modified) so that current will be less than a few mA

 

That's a simple way if the switch contact transfer time is sufficient to generate the desired pulse width.
Typically I would expect that to be only a few ms.
You could stretch that time by adding a diode and capacitor on the output.

I was thinking it might suffer badly from switch-bounce, because the bounce times would be quite long compared to the pulse width so I was thinking of tidying it up with a 555 monostable.