Hello, I've been visiting this site so much over the last year. I'm studying a level 3 btec extended diploma. I'm currently in my 2nd year and working on my project.

My project is to make a security light which is triggered by a hb100 microwave sensor but I'd like to add more variables with an arduino aswell, such as the light will only come on if the sensor detects movement and another condition is also met, such as the time and a pir sensor. However I'm in the early stages and struggling with the preamplifier. My teachers are confused by my project in think they are put off as they have never seen this sensor before.

I have built a 2 stage preamplifier using a lm324.

I have tested the amplifier by applying a 100hz signal at 30mV, and observed around 2.5V peak to peak output.

Am I right in thinking I should be seeing 5V output for the amplifier stage so the arduino can work with the signals?

Also I am having a problem when I connect the microwave sensor. The output signals are still tiny, in the mV range.

Many other projects I see have a VOUT and FREQ OUT. however the documentation for the HB100 only specifies OUTPUT... I'm assuming it's frequency.

I have seen projects done with this sensor before and I'm still unclear, I hope there is somebody who can explain why I am only seeing tiny signals on the output when the circuit is in operation, as that is my main challenge.

I cannot seem to upload my pictures from my phone, I'll upload the documents I am using, now.

Thanks

 

The op amp is biased at 2.5V half supply, so your signal will swing about that point, reading the datasheet, the sensor gives out microvolts, and works on the principal of the Doppler shift, the faster the object moves the bigger the frequency of the output signal.

 

You tested the amplifier with 30mV @100Hz?

Isn't the output of the HB100 a matter of uV (microvolts) according to the datasheet?

Did you build your own preamplifier or use the one on the datasheet?

 

Some Shields for the hb100 i have seen have a FREQ OUT and VOUT but the designs they are using surely must be different from the design notes.

I built the exact amplifier as in the datasheet for continuous wave.

Yeah I used 30mV @ 100Hz at the input and seen 2.5V at the output with the oscilloscope. Increasing the Vin caused some clipping of the sinewave after 2.5V which I expected.

I am expecting the microwave sensor to output very small signals into the preamplifier, but I should surely see much larger amplitude at the output of the 2 amplifiers?

I will be testing this again tomorrow evening after work but I only have a small arduino based oscilloscope at home. I will keep this thread alive as I'm sure my work will help others, I'll work on getting my images together in think I have to upload them to Google drive 1st.

Cheers for the replies I hope you can further help

 

I don't see where it says it operates in micro volts in the datasheet. It would explain alot if I got my units mixed up though. I'd be really dissapointed in myself Haha. I have had a look at another datasheet and there is some mention of uV although I don't understand it completely. I'll upload it here.

Also this guy has got his working, looking at the oscilloscope his range is 2V per divison and he used the same schematic as me.

http://jpnelson.com/post/37623468093/microwave-motion-sensors-for-fun-and-profit-hb100

 

it operates in micro volts

A bit of math shows the amplifier to be working between 3.3 Hz and 72 Hz. The maximum input signal to the amplifier) would be about 400 microvolts.

 

I don't see where it says it operates in micro volts in the datasheet.

Top of P3 of the App Note linked in post #1.
You will need extremely good screening of the amplifier, and careful attention to pcb layout etc, to avoid the desired signal being swamped by interference.

 

Thank you very much, guys. I'll look more into the the operating frequency of the amplifier, I'm not 100 percent sure of its relevance at the moment as we're only just beginning to look at analogue devices.

I'll keep posting my findings here and hopefully others will benefit from it.