In the last blog I expressed wishful thinking in that the board that we printed would just work. As the norm is with hardware, that was not the case. The board that we printed had several issues. The main being that we had designed the board in fritzing as if we were plugging components into the bottom (copper) side of the board. This means that the entire board was flipped (in the y direction) to what it should be. The way to fix this will be to flip the board using the tool inside the CNC machine software. Fritzing gives no easy way to do this, so the CNC software will be much more effective.
The other problems were that we had incorrectly placed our resistor. The correct placement of the resistor is between the power pin and the readout pin on the DHT sensor, so that the resistor can act as a pull up resistor to the power. We are planning on writing a digital pin HIGH to send the voltage to the sensor. Therefore, instead of the sensor power being connected to the VCC pin on the arduino, it will be connected to a digital pin and controlled through the code. The sensors were also wired opposite of each other, so we need to make them consistent for our sanity.
Lastly, there was some issues for the Wifi chip. There were questions about which way that it was connected to the board (orientation wise), and although RX, TX, VCC, and GND were correct, the other pins (GPIO_0, GPIO_2, and CH_PD) were all question marks to us. It turns out that these pins should all be connected to power to avoid floating pins (although they can be left floating, it is better to have them written HIGH).
We have redesigned our board to accommodate all of these changes (barring the flipped board because we will have to do that when we print the board). The way that I did it was by only working in the PCB tab of fritzing rather than the breadboard, and deleting any ratsnest wires in the schematic tab. It makes so much more sense now as I can explain each and every one of the connections. The only concern that I have is that we have not tested whether or not a sensor can be powered from a digital pin. In theory, there should be plenty of current for the sensor, however, since we do not have a working prototype this worries me.
In the meantime, we have created and presented our posters for the Service Learning Expo at Berea. We did not make a Fritzing poster because it is such a small part of the project. Instead, I focused on the WiFi poster (which was my original group). This allowed me to talk about both the ESP8266 and the PCB because I was able to stand in front of the “generic” poster for the PCB. It was a great experience overall and I am excited to reprint and test our board and see whether or not it will work.