Update on myDAQ accoustics - myBAT

As stated last week, we needed to work on the AA Filter to improve the filtering.  We did this by tweaking the resistor values and capacitor values until it satisfied our specification.  The datasheet for our Electret microphone reads that it works well until around 66 kHz but goes quite weak to signals above this value.  Therefore we needed an AA Filter which would cut off at approximately 66 kHz and as the myDAQ has an upper limit of 100 kHz, we needed it to attenuate at approximately 100 kHz. 

The pictures below show the frequency response of our AA Filter.  It initially starts at 24 dB and at 21 dB the cut off frequency is approximately 64 kHz shown in the first picture, at 100 kHz it attenuates by approximately 34 dB shown in the second picture.

We were satisfied with our results as they matched our specifications.  The picture below shows the AA Filter built on the breadboard and connected to the myDAQ.

We decided that it was time to start on our final design.  As we are now going to do the shifting on labVIEW there will be less hardware.  Using Altium, we designed the schematics and PCB layout for our final PCB (shown below). We then sent it in to be manufactured.  As you can see from the schematics there are four operational amplifiers.  Three of them are for the AA Filter and one is for the pre-amplifier.  We strived to keep the circuit to four operational amplifiers as we could use a quad operational amplifier chip resulting in less space used as well as less complexity.  This would also help for future students to build this design.

Whilst working on this task we soldered our microphones onto the PCB that we built earlier.  The final parts that we were waiting for have arrived and we have soldered them.  We are going to start testing very soon.  Final PCB for the first design is shown below.

After submitting our design for the final PCB, it was manufactured within a day.  Below is a screenshot showing the PCB after it was manufactured.

We started soldering shortly afterwards.  As this PCB is smaller and has fewer components than the last one, it was reasonably quicker to solder.  Below is a picture of our final PCB.

We have soldered in the microphone and  the wires to connect to the myDAQ.  We wanted the wires to be like this so in the future if we wanted to add more to it or more PCB’s we could connect via the wires.