Radar project, video amplifier is not working

[rmmstn]

Hi,

Currently, I am working on a radar project which is given me and it can be found from mit opensource.(I am also attaching the schematic here). However, when I build this circuit, Im having a trouble with video amplifier stage. First of all, when I give +12volt from the ic's 4th node, my ic is getting very very hot so I disconnect it not to be burned. I checked its datasheet, it is showing for -+5.25v voltage range, too. I couldnt get how it is seen convenient to give +12v. What am I missing? Whenever I pass about 5.5v, the chip gets warmer. Also, how can I design an alternative? I need to know Rin and Rout for video amplifier right?. How can I find it out? (Input is coming to this circuit from a microwave circuit with -28dBm power)

If you can help, you may kind of save a life.
Thank you

 

[barry]

MAX414 is rated for 12V absolute MAX. Suggested maximum is 10V. The chip might be damaged. But I have to ask, why would you be applying video to the audio input of a laptop?

 

[rmmstn]

Video amplifier has two stages there as you can see. One is filter which I need to use to prevent pc alias. According to my investigations, sound card of the laptop is 22kHz so I need to put it not to send something above that. The other one is gain stage which I need to use to see better monitoring results on pc, I believe. The signal will be sent as an analog signal then it will be converted to digital one by pc to be processed as a .vaw file. Matlab will be used for that. Thus, I think sending it from audio port wont give any problem. That is what I know actually. Chip is coming from far away, what can I do ? Do you have any suggestions?

 

[barry]

I wouldn't expect 12 V to damage the device since manufacturers are usually conservative in their specifications. But the fact that it got "very very hot" is not a good sign. I would just use an oscilloscope and monitor the output of each stage. Maybe use a lower supply voltage for your testing. If you don't get the expected output at each stage, then the device is probably no good.

 

[rmmstn]

Since I cannot get a nice respond from the chip I talked about, I have decided to build a new one on my own, and if we assume the output will go to the audio port of the computer, what should I take as the input impedance of the audio port, what do you think? On the internet, Im seeing very different values but there might a value which is fixed because headsets are compatible with these ports and I think that they are designed accordingly.

 

[CCNezin]

Hi, I also worked on the coffee can radar project, and I experienced the same issue - the chip would get very hot. So as far as I know, don't worry you're not doing anything wrong. Just a few observations we made - the chip only got hot when we put in new batteries. 10-30 minutes later the chip's temperature would reduce to normal. We think this is because the chip is not supposed to run quite at 12 V and after a while the batteries' voltage decreased a bit. After it cooled down, it all worked as intended - we got range and Doppler working. As for recording, it gave us a lot of issues as well. We ended up using the audio to USB adapter that you can buy from here. Let me know if you need any further help.