View Full Version : Propeller to LCD

Jon M
09-04-2007, 09:28 PM
Hi Guys,

I am linking a prop to a Milford Instruments LCD Serial backplate (which is very similar to the Scott Edwards ILM unit) and got the old problem of 3.3v signal from Prop to a 5v signal requirement on the Serial board. Has anyone done it and how..ĚThe PIC isn't tolerent of 3.3V signals so I need to boost the signal, what's the best/cheapest way of doing it without inverting the signal.



09-04-2007, 09:32 PM
Can't answer directly - though you might find the info' you're after in the first 'sticky' thread (http://forums.parallax.com/forums/default.aspx?f=25&m=124837).

Have you tried it? I mean; will the LCD accept comm's at 3.3V (might be high enough to trigger the logic...)?


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You'll always have as many take-offs as landings, the trick is to be sure you can take-off again ;-)
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David B
09-04-2007, 09:42 PM
The way I've driven a 5V Scott Edwards LCD is to use an ordinary 5V IC having a Schmidt input, like a 74HCT14. The 3.3V propeller output is able to fully switch the Schmidt input, and the IC emits 5V from its output. The IC has 6 inverters, so you could either use a second inverter to invert the inverted output from the first, or you could edit the propeller code to pre-invert the LCD signal before sending it to the logic chip.


09-05-2007, 02:06 AM
Yesterday I got my 5V HD44780 20x4 LCD unit working with the propeller by driving its VDD directly from my propeller's 3.3v regulator. With this arrangement I just tied the prop's pins directly to the display since they are running at the same voltage. The display seems to work fine with no issues. I've been able to display text data with no problem. The HD44780's datasheets says the minimum voltage is 4.7V, but mine doesn't seem to care that's it's being driven 1.4 volts below it's rating.

09-05-2007, 03:06 AM
I also had never problems with a variety of such kind of displays...