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• TI Thinks Resolved

Pulse Width Detector Circuit

Greetings to all,

Hi, I have a mini project that needs to me design a circuit that detect pulse width of 10% and 20%, with input signal of 10ms clock period signal. Second of part of the project is to convert the 10% input pulse width to 60% and generate 5V if the circuit detected 20% input pulse width.
I do know that I have to use 555 timer to convert the duty cycle but I am having trouble designing the pulse width detector. My approach is to use a counter to detect the input pulse width, is that correct?

• Hi Vake,

The simplest approach would be to use a low cost microcontroller such as the MSP430FR2000 and just program it to do what you want.

If your goal is to do this with logic ICs, then I would recommend taking a close look at monostable multivibrators (MMV) such as the SN74LVC1G123 and D-type Flip-Flops (DFF) like the SN74HCS72-Q1.

Here's a circuit I designed not too long ago to determine if an input pulse is a certain length:

The MMV produces an output pulse of a set width when the input has a rising edge. The DFF is triggered to change the output state after a set time period, which will match the output to the input signal -- if the input signal is still high (ie the pulse width is too long), then the output is HIGH, and if the input is low already (ie it is shorter than the given time period), then the output will be LOW.

The Logic Minute training page has videos on many interesting topics that all are kept shorter than 5 minutes.

• In reply to Emrys Maier:

Hi Emrys,

Thank you for replying, but I have to design a circuit using IC chips. I was thinking of using a 555 timer to generate my own 10kHz clock pulse and a synchronous counter of 5 JK FF to detect 20 pulses during the 20% duty cycle of 10ms. Once it detect 20 pulses, the circuit will then convert the input signal to another 555 timer to convert it to 60% duty cycle. Is that possible??

• In reply to Vake:

That might be possible - I know the 555 timer is a versatile chip and can be configured many different ways, however I am not one of TI's experts on that chip.

I would recommend reading the datasheet for the 555 timer as well as any application reports you can find for the desired circuit(s). I know there are dozens of websites with detailed information on how to use the 555 timer, so you should be able to find quite a bit of useful information.

You might want to take a look at counters: http://www.ti.com/logic-circuit/specialty/counter-arithmetic-parity-function/products.html#p404=Counter&p1498=Catalog

The Logic Minute training page has videos on many interesting topics that all are kept shorter than 5 minutes.

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