634 displaying garbage with TTL input


New member
My serial based 634 LCD works fine when connected to my computer.
However, when JPE is closed, and the LCD is connected to a wireless serial link (BlueSMiRF), which outputs 0-5V, I only get garbage. The wireless serial link is set to 19200, the same as my RS-232 connection.
I've tried sending characters from both Wintest and hyperterminal (using 8n1).
Any ideas?
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New member
Although I havent tried closing JPB, I don't think thats the issue.
When repeating the same character a number of times, a number of characters are repeated, though not in any discernable pattern. It suggests to me that theres some issue with the baud rate, but I've already tried everything I can think of, different baud rates, querying the BlueSMiRF to check what baud rates, parity and stop bits its using, etc.
I'll try JPB sometime in the coming week, and let you know how it turns out.


New member
Hooray! it works!
Thankyou soooo much :)

Out of curiosity - what in the datasheet suggested to you that the logic should be inverted?

CF Tech

The UART pin on a micro is typically connected to a "MAX232" level translator type device. The level translators invert. So if your signal comes to the LCD without going through a level translator, it looks inverted to the LCD.
USB LCD Displays - Graphic and Character LCDs with a Keypad