Tweet
Hello I am experimenting with homemade Quasar ARM detector and noticed that unit shows coil balance a lot higher than on oscilloscope. According to the detector it is is close to 300mv when scope indicates a 10-20 mV peak to peak. Could it indicate voltage after the preamp amplification? My suspicion is that the preamp gain is way to high due to some error. Trying to troubleshoot it but have difficultie understanding how RX preamp in the given schematic works. Confusion is mostly about the SIN_C input witch supplies sinusoidal waveform of the same frequency as detector operates. Could someone direct me to read about such op amp configurations or shortly explain the idea behind such design? Many Thanks!
-
-
SIN_C is output from processor so probable a Square wave (Logic high or low) and not an analog sin wave.
You need to look at the STM32's code to see what this actually does and when.
The receiver gain amp is a typical op-amp gain with AC coupling, Zero is an offset bias then the SIN_C summing.
The schematic as posted is very hard to read, resolution has been lost. A PDF file would probably be much better.
-
Sorry for low rez. schematic. I am attaching a full scale pdf. Sin_C is sine wave from internal DAC output for sure. Unfortunately only the hex file for STM is available no code.Comment
-
Much better schematic. thanks.
Ok, SIN_C is a DAC produced sine. Is the TS signal also a Sine or a square?
If TX is Sine then the RX amp is summing a reference Sine with the rx coil signal. This should produce the difference due to phase shift
Try putting circuit into LTspice to learn what it does based on measured signals.
what is the TX and SIN_C Frequency??
Comment
-
Tx is a square wave both at 10khz. Will try Spice simulation.Comment
-
Hi Batonas,
Can you post up the Hex file for this project as I believe it is open source but I can only find the PCB and SCH files on the web.Comment
-
Here is the newest hex file and link to creators site with all firmware versions and most other information in russian.
https://fandy.ucoz.org/publ/metalloi...m_quot/2-1-0-5Comment
-
So I think I have preamp (mosty) figured out. U1A works as a differential amplifier and sin wave is used for coil balance compensation. Coil balance voltage measurement done by the unit is still unclear.Comment
-
Yea, that signal goes into the STM32 so it is the CODE that handles this.
Without good commented source code it is just a Black Box.Comment
-
The sync signal is fed from the microcontroller to the RX stage to compensate for residual unbalance. The microcontroller outputs a sinusoidal signal. The compensator in the Quasar metal detector works only when you press the unbalance auto-adjustment button. And that's all. Unbalance compensation is not activated automatically for a long time. It only works in manual mode when the user decides to perform this operation. The source code for Quasar has never been and never will be in the public domain. Only encrypted hex files for firmware.Comment
Comment