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Can any one help me with a circuit that will take the squarewave produced by a Memsic 2125 Dual-Axis Accelerometer into a lm2907 to give a 0 to 5v analog output.
The LM2907 isn't the best device to use for this although it might work. It is really a frequency to voltage converter rather than a pulse width to voltage converter but it does use an internal charge pump so the output will change with PWM ratio. The output wouldn't follow the manufacturers data sheet which expects a constant pulse width and variable frequency so predicting performance would be difficult.
This is a copy of the original circuit that I would like to replace AC1 and AC2 with the Memsic 2125. The LATACC and FACC are a analog 0 to 5v signal which are fed directly to a 68HC11 micro.
Sorry that there are no part numbers or values on this drawing, I have not had time yet to identify every component on the original PCB.
I have never had to convert a PWM signal into a analog signal before so all this is new to me.
This shows a recommended single pole filter. Note use of PWM as a DAC has an
undesired (generally speaking) latency. So if you are trying to use this in a real
time control loop it can be a significant effect on control loop response. The
alternative is to use the processor to do a direct pulse width measurement, although
that too has a significant latency due to PWM pulse width fairly long, eg 2.5 or 10 mS.
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