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TTL to Analog Display???

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Squintz

New Member
I have a GPS system with a TTL output that generates a pulse every 2.5mm (400 pulses per Meter). I need to Somehow convert that to an analog output and feed it to my Falcon DPM952-T Panel Mount Digital Multimeter. On the multimeter display it needs to be in units of Mph.

Please ask questions if i have not given you enough information.
 

ljcox

Well-Known Member
TTL to Analogue display

I don't understand what you mean by "a pulse every 2.5mm (400 pulses per Metre)" However, I assume that you want to convert a pulse rate to an analogue value.

The way to do this is to use a monostable followed by a low pass filter.

The monostable generates a squarewave signal whose mark/space ratio is proportional to the pulse frequency. The low pass filter (a resistor and capacitor) creates an analogue voltage that is proportional to the average voltage of the square wave signal which is thus proportional to the input frequency. To scale the output in mph, all you need to do is to include an amplifier with the correct gain.

See the circuit I posted - Phase Detector, on 27 January 3.19 pm {Australian time (GMT + 10)} If you replace the XOR gate with a monostable, it is essentially what I described above.

There is also an IC that converts frequency to voltage LM2917, from memory, this does essentially what I described above.

Len
 

Russlk

New Member
Since you already have pulses, it is only necessary to low pass filter the GPS output. You may want to amplify the pulses first to minimize the DC gain required to drive the meter.
 
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