# Monostable multivibrator

Discussion in 'General Electronics Discussion' started by Bekzat, Feb 20, 2017.

1. ### Bekzat

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Feb 20, 2017
Hello, working on project where I need a monostable multivibrator.
The question is: How can I make two unstable and one stable states, like +vcc and -vcc are unstable and 0v is the stable one. Example: if Positive triggers it goes +vcc for a wile and comes back to a 0 volts, else negative triggers output goes -vcc for some time and comes back to 0 volts

2. ### AnalogKid

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Jun 10, 2015
That is not a normal monostable, but a standard chip or circuit can do that with some extra parts. You don't say if the two pulse periods need to be exactly the same, or only within 10%. Off the top, one approach:
Input goes directly to one monostable with negative input protection, and to a bipolar inverter that drives a second monostable. Output of the first pulser is the positive output pulse. Output of the second pulser goes to a bipolar inverter to make the negative output pulse. Sum the two outputs into a common bipolar output driver.

1. Are the output pulses longer than the input pulses. In other words, does the input trigger signal return to 0 before or after the end of the corresponding output pulse?

2. What is the load? How much current does the output need to deliver?

3. What is the speed? What are the maximum rise and fall times of the output pulses?

4. What are the values of Vcc (the positive supply voltage) and Vee (the negative supply voltage)?

5. AND - what are the output pulse widths and tolerance?

ak

3. ### Bekzat

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Feb 20, 2017
Output pulses are longer than input

The load is DC gear motor 6vdc, the current is around 0.11A
-Vee is for the ccw, +vcc for cw

I need output signal time around 5s

+9v and -9v

Depends on timing, say it is 5 seconds

Thanks
If you can help me with this, would be great!!!

Last edited by a moderator: Feb 21, 2017
4. ### AnalogKid

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Jun 10, 2015
6.
a) All solid state solution
b) All relays and diodes
c) Solid state control of relay output stage?

ak

5. ### BobK

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Jan 5, 2010
d. Microcontroller and 3 MOSFETs (half bridge and level translator)

Bob

6. ### AnalogKid

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Jun 10, 2015

Bekzat - do you own, have access to, or have ever used a microcontroller software development system and device programmer?

Bob - won't you need two level translators?

ak

7. ### Bekzat

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Feb 20, 2017
Yea I have an access, but it is analogue project. Requirements are pure electronics without implementation of a microcontrollers

8. ### BobK

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Jan 5, 2010
With the supply at 9V, yes, you would need two level translators. I was thinking 5V supplies.

Bob

9. ### AnalogKid

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Jun 10, 2015
Are open collector output ok, or do you need the output to be driven back to 0 V after a pulse?

ak

10. ### Bekzat

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Feb 20, 2017
Yes I need output to be driven back to 0 volts, in this state the motor will not turn

11. ### AnalogKid

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Jun 10, 2015
But - the motor also will not run if the output goes to a high impedance, such as an open collector stage that is turned off.

What is it you want to achieve? How many motors are there, are they uni- or bi-directional? Etc?

If the idea is that there is one motor that runs in one direction with a positive input pulse and in the other direction with a negative input pulse, it's kinda important to know that because it changes the output stages. Also, SPDT relays are perfect for that kind of operation, but we don't know if relays are acceptable. See post #4.

ak