Update on myDAQ accoustics - myBAT

This week we started testing our PCB’s.  However we came across many problems.  The first being that there were some occurrences where the manufacturing process had not connected the wires in the right places.  As you can see below we had to add wires in ourselves to connect some of the components correctly.

1.      This wire connects the power terminal to the VCO 

2.      Pin 11 on the VCO connected to a resistor as it wasn’t connected to anything prior 

3.      Potential divider resistor (R26)  connected to one of the op amps 

4.      Capacitor C1 connected to resistor (R3) 

5.      Capacitor C3 connected to resistor (R7) 

6.      Capacitor C3 connected to via and then to transistor (Q2) 

7.      Capacitor C18 connected to MOSFET (Q4) 

8.      Capacitor C18 connected to pin 2 of audio amplifier 

Listed above are some of the problems we had which we have now fixed.  However, when we send a signal through the board, we can only find the signal up to the pre amplifier and the switching mixer.  Below are some pictures of the signal going through each of the stages in the circuit.

Firstly when we connect the board to 5V, the VCO sent a signal which had a frequency of approximately 49 kHz (this could be tuned to a value we desired).  This is shown below:

Next, we used the VCO output and fed it into the flip flop. The picture shown below is the output of the flip flop.  It is almost half of the signal from the VCO.

The next stage we checked to see whether the input signal was feeding into the transistor amplifier and into the transistor.   This signal was basically the signal we fed in straight from the function generator.  Although this was not a problem we have added it to show the stages of the circuit.

The output signal from the transistor amplifier was fed into the switching mixer along with the output signal of the flip flop.  At this point the signal that was passing through and the input signals had a lot of noise.  The output signal is shown below:

This signal was then fed into the operational amplifiers which amplified the signal but the signal was then saturated.

The next stage was the audio amplifier, this didn’t give any amplification and there was a lot of noise.

After a lot of fault finding we were unsuccessful and we decided that if we had time at the end of our project, we would come back to this as we needed to start testing our final PCB.  We felt it was unsuccessful because we were getting some graphs on the oscilloscope that we didn’t expect.  Also a lot of noise which we didn’t want which shows it is incorrect.

We have a labVIEW program that works correctly; it can shift the captured signal from a high frequency to a frequency in the audible range.  Initially we were taking steps with our labVIEW program and testing it on the PCB along the way.  At this point we decided to focus on finishing the labVIEW program.   As we started to test our PCB, we realised it wasn’t working as expected.  The +15V and the -15V were short circuiting as were the ground and the 5V.  Also the operational amplifiers were shorting out.  We could not comprehend why our PCB was doing this and so came to the conclusion that maybe because the +15V and -15V had thin connections on the PCB that the board must have been damaged, therefore we have decided to re make the PCB.  This took one day to complete.  This now works and a video of our PCB in action will be posted shortly.