Easy HB100 Amplifier

Building a Low Cost Amplifier for the HB100 Doppler radar Module 

Introduction:

The HB100 doppler radar module is a widely available low cost unit useful in many DIY projects and prototyping applications for systems that need to record the relative speed of large objects such as passing cars, people, or bikers. The unit comes as shown below, outputting a 10.5 GHZ RF signal towards approaching objects and receiving the returning signal, outputting the difference in frequency caused by the doppler effect through an integrated mixer. 

However for the unit to be useful the output of the signal must be amplified and read into the analog input pin of a microcontroller so that the FFT can be taken to calculate relative speed.  A complex amplifying circuit is suggested in the datasheet for the outputted signal that may be inaccessible to a hobbyist, or anyone looking prototype quickly, so in this project I aim to demonstrate a cheaper and easier make “Good Enough” version of the amplifying circuit that still provides a usable output for the typical 0-5V range analog input pin for widely available microcontrollers. 

System Description:

This circuit performs the following functions:

• Offsets the signal +2.5V 
• Amplifies its max 100 mv output to span the 0-5V range
• Passes output through low pass filter with 500 hz cutoff 

In the diagram of the circuit below from Left to Right: 

• A unity gain offset of 2.5V in the first Op Amp 
• Differential amplifier with a 2.5V reference amplifies signal to span 0-5V
• A simple 500 Hz cutoff low pass filter 

Parts List:

Resistors:

• 1K - (5x)
• 25K - (1x or series combination adding to 25K)

Op Amps

• OP07

Capacitors: 

• 330 nf (Or parallel combination adding to 330nf)

Other: 

• Breadboard
• 22 AWG Solid Core Wire 
• HB100 Radar Module 
• 5V Power Supply & Oscilloscope OR microcontroller for troubleshooting

 Step By Step Build:

Follow these steps in reference to Attached Image:

• 1: Grab all parts listed above

• 2: In the numbered order given in the image and paying attention to color coded values, place the resistors, then the OP07’s, then the capacitor 

• 3: Strip solid core wire jumpers and make connections as seen in figure 4 and cross check to Figure 3 to ensure accuracy 

• 4: Connect output of HB100 to circuit as shown 

• 5: Connect output of amplifier to your oscilloscope probe for testing or Arduino analog in pin for FFT operation.

• 6: Connect power and ground of your microcontroller or power supply

• 7: Connect HB100 5V and ground to circuit rails.

• 8: If moving on to using arduino after verification, use example FFT code here:
• https://github.com/TMRh20/AnalogFrequency/blob/master/examples/HB100/HB100.ino