LOGIC PULSE TRAIN TO VOLTAGE

John Brownhill's picture

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Joined: Oct 28, 2020

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LOGIC PULSE TRAIN TO VOLTAGE
October 28, 2020 - 3:51pm

Hi,

I've been looking for some time for a circuit that would convert a train of logic pulses with a frequency of 100 hz into a voltage maybe 0.1v per pulse up to a maximun of 7.8v @ 5mA and hold this voltage for up to perhaps 10 minutes( the conversion need not be that accurate ) .Then reset when another train of pulses is received to give another voltage.

John

Sourav Gupta's picture

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This could be easily done using mcu and dac... Are you looking for analog one?

John Brownhill's picture

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Hi,

I would be interested in the easiest way I only need a rough conversion.

Thanks

John

Sourav Gupta's picture

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What will be the voltage of the logic high?

John Brownhill's picture

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Hi,

The logic pulses are 0 to+1.5v lo  +3to+30v high

Thanks

John

Sourav Gupta's picture

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The best way is to use  microcontroller and a DAC. Programme it as a pulse counter use timer fuction to hold the mcu output. The DAC will produce the required output voltage. Since the input pulse is higher in terms of mcu voltage, a divider can be used. Also, an additional op-amp maybe required for the dac output to amplify the voltage to the required level.

The circuit will be simple, cost less, and you will find a lot of headroom. The drawback is you need to write the code and programme it.

John Brownhill's picture

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Hi,

Is there another way without using a microcontroller I have no experience using them.

Although I can build circuits I have no experience designing them which is why I posted this request on this forum.

Thanks

John

Debashis Das's picture

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You can try using a 555 timer to generate a PWM signal, then try to pass it through a RC Filter, as for RC value there are many online calculators available for you to try.

Michal Podmanický's picture

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Use some of counters IC (depends on desired resolution) and connect R-2R ladder to its output as a DAC.

 

 

John Brownhill's picture

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Hi,

I’ve been doing more thinking about my problem it seems the difficulty is the reset upon the next train of pulses.So I came up with this thought, a simple circuit to generate a stepladder output 0-7.8v.in 20 steps, and  when 7.8v is reached the circuit will reset to “0”

The idea being – I input 10 pulses = 3.90v then I need to change the voltage to1.95v which needs 5 pulses so I input 15pulses which raises the output to 7.8v whereupon the circuit resets to “0” then counts the additional 5 pulses. (the short time overshoot being unimportant)

I looked at digipots DAC ics R2R but was unable to find one (an up down one ) that would reset to zero the ones I saw only reset to half value.

John

Michal Podmanický's picture

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There are many ways how to do it.

A few:

 

1) Timeout. Lets say you enable 100ms time window to read from 1st pulse to 10nth. After 100ms every other pulse will be considered as new reading of all train(and reseting). Basic monostable with LM555 to obtain single time window will do the job.

2) Send one wide pulse, which will represent a reset state.

 

The idea about adding pulses to reach reset isnt quite good due to case of losting pulse (1 bad pulse can collapse everything).

Michal Podmanický's picture

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Relating to R2R, i didnt see your desired resolution. Now i see it is about 78. (7.8v/0.1v). In this case, use a counter IC connected to DAC IC.