Hello guys,
I recently got an HB100 which is a Doppler radar for opening door.I made the circuit that comes with the application notes which is just amplification and a comparator,so i connected the output of the comparator to the pin 8 of my arduino and used the freqmeasure library to get freq but alas no reading.
I cant figure out why its not working.Just hoping i made a dumb mistake and its not broken.
I wonder what a "1m" resistor should be. 1 milliohm looks too small to me, and 1 megohm too high with respect to the resistor on the inverse input. Which value did you chose?
1M(Mega) think they just missed the shift key xD
clezv:
1M(Mega) think they just missed the shift key xD
Then they missed that key twice 
Do you have a scope, to check the circuit?
If not, an audio amplifier or piezo earphone or buzzer may work as well, for the AC signals.
The output from the module is an audio signal in the microvolt range. This means that the output needs significant amplification for it to become useful. The LM324's are not being used as comparators but as band-pass audio amplifiers. The first LM324 is configured as a non-inverting amplifier with the gain set by the 1M and 10K resistors. The 2.2nF capacitor provides the high frequency roll-off and the 4.7uF to ground provides the low frequency roll-off. In the second, the LM324 is configured as an inverting amplifier, the gain is set by the 1M and the 8.2K with the 4.7uF and the 2.2nF doing the frequency roll-offs. The gain of each stage is about 100 or 10,000 both stages combined.
This module is a doppler module and output only occurs when the target is moving towards or away from the module. If there is no relative movement to the target, there wll be no output from the module and no output from the amplifier. To test you need to have a moving target. Wiggling your fingers on front of the beam will do no good because the forward and backward movements cancel each other out.
I suggest using standard audio amplifier testing processes to ensure that both stages are working and then set up a walking target. You should get an audio signal near 100Hz for a human walking at a normal speed.
Take care with shielding during construction to minimise hum and noise in the high-gain audio stage or stray signals will affect the results.