Newhaven Display Forum

Okay, in case any other amatuers find this thread I solved my own problem. It turns out PC's serial ports use RS-232, but the voltage for a HIGH signal is negative (on my computer it's about -6V). I need a chip to translate the PC's RS-232 signal to TTL logic levels. I found this useful post about it:
https://www.sparkfun.com/tutorials/215 using a MAX232 chip to convert PC rs-232 to TTL levels the display will be able to use.

I connected this screen to my PC using a USB to Serial interface, custom DB9 connector wired as shown in the manual. I am using RealTerm to send hex numbers to the screen and I get characters that don't match up with what is on the chart. For example I send 0x21 and screen prints 'u', 0x22  = ':', 0x23 = 't'.
One post mentioned to make sure voltage is at TTL level. See attached for how I have it wired up. On J1 I have Pin1 connected to Pin 3 on the DB9 (rs-232 TX), Pin 2 connected to DB9 Pin 5 (GND) and Pin 3 connected to 5VDC which I get from a different USB cable I have cut and stripped. I measure 5.08 V across pins 2 & 3 on J1.
After playing around with it for awhile and getting characters (but not the right ones) I may have fried it because now it only shows the characters shown on the screen and no longer responds to any commands. I ordered another one which I should receive tomorrow. Let me know what I may be doing wrong. I am testing now but I would ultimately like to have an Opto22 PAC controller sending messages to the screen.

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