I need to connect a PC to my washing machine. The washing machine has a bank of pins labelled like this:
- 0v
- tx
- rx
- 5v
The microcontroller is an ATmega32L, which has specs for the serial connection as follows:
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) is a highly flexible serial communication device. The main features are: • Full Duplex Operation (Independent Serial Receive and Transmit Registers) • Asynchronous or Synchronous Operation • Master or Slave Clocked Synchronous Operation • High Resolution Baud Rate Generator • Supports Serial Frames with 5, 6, 7, 8, or 9 Data Bits and 1 or 2 Stop Bits • Odd or Even Parity Generation and Parity Check Supported by Hardware • Data OverRun Detection • Framing Error Detection • Noise Filtering Includes False Start Bit Detection and Digital Low Pass Filter • Three Separate Interrupts on TX Complete, TX Data Register Empty, and RX Complete • Multi-processor Communication Mode • Double Speed Asynchronous Communication Mode
My USB to TTL serial adapter is apparently based on a ch340 chip. It looks almost exactly like the pic I attached, except mine does not have a crystal on it because I think the chip has an embedded clock. The important thing is the pins match my adapter.
My knee-jerk thought was to connect it as follows:
adapter → washing machine PCB
gnd → 0v
rxd → tx
txd → rx
3v3 → (nothing)
5v → 5v
(with s1 jumped to 5v on the adapter)
Someone told me I should not connect 5v to 5v. I was assuming one connection needed 5v and the other supplied it, but I was told they are both supplying 5v, but not perfectly 5v, so the difference will strain something and cause damage.
So how should I hook this up?
residentoflaniakea@discuss.tchncs.de 1 week ago
If they both are power supplied, and have ground connected then what would you need the 5V connection for? Some devices that externally supply power can come with a protection diode to prevent looping power back to prevent the scenario you described but looks like that’s not needed. You would have to know the protocol used such as baudrate, bitlength, stopbits and parity. If you don’t have that info try common baudrates (115200), 8 bits, 1 stop, no parity.
perestroika@slrpnk.net 1 week ago
Note: another really common baud rate is 9600, 8, 1.
diyrebel@lemmy.dbzer0.com 1 week ago
I had the two 5v pins connected (from 5v on the adapter to the 5v pin on the washing machine). I had it that way for maybe 10 or 15 min until I was told not to. Now I wonder if I damaged it because when I meter the 0v against the 5v, there is almost nothing there. Did I damage it, or did the manufacturer disable the serial port before it got to me?
residentoflaniakea@discuss.tchncs.de 1 week ago
Hard to say, but if the 5V natively to the machine is shot, I’d expect the unit to not work as its systems would depend on it. I assume you measured 5V in reference to the machines GND. Double check your meter against a known good 5V supply (your adapter).