User:Riviera/Breadboard to circuit board
In preparation for Special Issue 24 I have decided to make a piece of hardware. It involves two circuits: one is digital and one is analogue. On the one hand, the analogue circuit employs a 555 Timer and a LM386. I wired up four resistors and four capacitors to these integrated circuits to create a Voltage Controlled Oscillator (VCO) and an amplifier. Three of the resistors are photosensitive (LDR). The circuit creates a sound when a battery and speaker are connected. The sound changes in accordance with the amount of light hitting the LDRs. On the other hand, the digital circuit features an ESP32 microcontroller which is connected to three LEDs. The ESP32 functions as a WiFi access point. It also hosts a website which can be visited from phones, tablets or laptops that are connected to the access point. The website features three sliders which adjust the brightness of the LEDs. Each LED is positioned inside a tube and at the other end of each tube is an LDR. That is how the digital circuit interacts with the analogue circuit.
It took some time before things started to work as expected. The amplifier was simpler to create than the VCO. I was able to produce a sound, although a conversation with Nan Wang at the Interaction Station revealed I was amplifying noise, not a signal. Initially, I speculated it would be possible to use the microcontroller to vary the supply voltage to the analogue circuit. Nan pointed out that doing so would be redundant and perhaps even impossible. As Nan put it, ‘the Arduino is not the muscle, it’s the brain’. I was also informed that the circuit I had designed featured passive components only. Indeed, I had omitted a potentiometer in the VCO as I did not realise this was a mandatory component. This was one reason why the circuit was not functioning as expected. Nan advised that it’s best to watch videos, on YouTube for example, when creating analogue circuits, rather than working solely from schematics. This is because the schematics themselves may be faulty and the audio-visual support offered by a video proves the circuit works as it should.
In general, I began by prototyping the circuits on breadboards using jumper wires. Then I used solid core wires to flatten the design and get a better overview of the analogue circuit. Subsequently, I recreated the breadboard in Fritzing. The advantage of using Fritzing is that one can switch between breadboard, schematic and Printed Circuit Board (PCB) views of the circuitry. I asked Joseph a while ago if he had any tips on how to sort out PCB routes in Fritzing. He said he didn’t have any, other than using the autoroute feature and that it simply takes time. Therefore, I set about positioning the analogue circuit components for a PCB with two layers. Had I used Fritzing’s services to fabricate three boards it would have cost 30 EUR with expedited delivery.
On June 13th I went to the XPUB studio and demonstrated the prototype to Wang. Wang said I should consider etching the circuit using one of the copper boards which Joseph had bought. The DIY approach was practical, inexpensive and took approximately half a day. I edited the PCB design in Fritzing, changing it from two layers to a single layer. Then, I printed the layer on a copper board using the flatbed printer in the Printmaking Studio. Throughout the day I went from station to station executing various tasks and asking questions. Having prepared the copper board, I had it cut down to size at the Metal Station using the guillotine. It was approximately 2.5” by 2.5”. Then I returned to the Printmaking Studio and placed the board in an ferric chloride bath. The process took about 45 minutes and stripped away excess copper from the board. I headed back to the Metal Station and used a 1mm drill to create 36 small holes so I could attach the components. At this point, I realised I would need to remove the copper from the other side of the board. I returned to the Printmaking Studio and bathed the board in acid again. I also found out it’s possible to use a CNC machine to etch circuit boards instead of using chemicals. Lastly, I soldered the components to the board.
I haven’t yet tested whether or not the board works as expected. I plan to do so on June 14th. Overall, I am optimistic. In the worst case scenario I will go back to the breadboard.
My next steps will likely include:
- Making an enclosure for the device out of wood.
- Making a circuit board for the digital circuit.