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# Timing circuit

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#### axujiec

##### New Member
Hi all,

I am building a remote laser distance finder. I need a timing circuit to find the difference between pulses for 2 photodiodes. One photodiode receives laser impulse right next to the laser. When the 2nd photodiode receives impulse reflected of the distant object. I am looking for time difference between those pulses of about ns. Circuit can output results on oscillator as 2 peaks or any other possible way.

Thanks.

You'd need a pretty good timer to measure timings in the order of nanoseconds. It'd most likely be very expensive.

Last edited:
Hi all,

I am building a remote laser distance finder. I need a timing circuit to find the difference between pulses for 2 photodiodes. One photodiode receives laser impulse right next to the laser. When the 2nd photodiode receives impulse reflected of the distant object. I am looking for time difference between those pulses of about ns. Circuit can output results on oscillator as 2 peaks or any other possible way.

Thanks.

hi,
What is the required distance/range of this laser, also the required accuracy.?

hi,
What is the required distance/range of this laser, also the required accuracy.?

Distance doesn't really matter, I was thinking about 50-300m. Accuracy of about 1-5m.

I was also wondering if its possible to measure distance using pulsating laser and 2 counters connected to nearby and far away photo diode. We would know the frequency of the pulses. 1st counter would count number of pulses and the second counter would time the experiment. For example if its on for a minute there would be certain amount of pulses counted. Since we know the frequency of send pulses it would give a delay.

This would avoid the timing circuit. However if the timing circuit is possible to build it would make the life easier

Thanks

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Laser range finders and target illuminators are used in the military who can afford buying that expensive stuff.

To measure distance it is advisable for a hobbyist to use sound.

Light (and so does laser) travels at 300,000km per second. Sound travels at 330m per second. So light travels at a speed 909,090.9090 times faster than sound.

It is much easier to measure a sound signal and gate it accurately with commonly used ICs.

Measuring in the range of 300m air density and relative humidity can almost be negligated.

Use ultrasound transmitters and receivers and build your timing and evalution circuit on that basis.

Measuring the distance between the earth and the sun it would make sense using light. If the sun decides to turn off its light it will be dark on earth eight minutes later.

Boncuk

Laser range finders and target illuminators are used in the military who can afford buying that expensive stuff.

To measure distance it is advisable for a hobbyist to use sound.

Light (and so does laser) travels at 300,000km per second. Sound travels at 330m per second. So light travels at a speed 909,090.9090 times faster than sound.

It is much easier to measure a sound signal and gate it accurately with commonly used ICs.

Measuring in the range of 300m air density and relative humidity can almost be negligated.

Use ultrasound transmitters and receivers and build your timing and evalution circuit on that basis.

Measuring the distance between the earth and the sun it would make sense using light. If the sun decides to turn off its light it will be dark on earth eight minutes later.

Boncuk

Yea, but I still need to use laser ultra sound would have been to easy. Then i need to make it detect velocity.

... suggestion

Use two lasers in parallel ..... a fixed distance apart.
If the two lasers are both focused on the target, then the acute included angles between the lasers, along with the laser separation distance will provide sufficient information to compute the target distance .....
The construction problem is then reduced to how precisely you can measure the laser angles.
... This is know as the parallax method of determining distance.

Use two lasers in parallel ..... a fixed distance apart.
If the two lasers are both focused on the target, then the acute included angles between the lasers, along with the laser separation distance will provide sufficient information to compute the target distance .....
The construction problem is then reduced to how precisely you can measure the laser angles.
... This is know as the parallax method of determining distance.

This is very good and easy to make thanks. However I cant extend it to measure velocity in any way.

Hi all,

I am building a remote laser distance finder. I need a timing circuit to find the difference between pulses for 2 photodiodes. One photodiode receives laser impulse right next to the laser. When the 2nd photodiode receives impulse reflected of the distant object. I am looking for time difference between those pulses of about ns. Circuit can output results on oscillator as 2 peaks or any other possible way.

Thanks.

How are you reflecting the laser impulse. Will each distant object in question have a reflector of some sort?

Yea it would have a mirror

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