BPI-216 LCD on Propeller trouble

gilabite

Hello hoping someone on here can help me. I have an old BPI-216 serial LCD that I used to use for Stamp projects and now I want to use for a Propeller project. But I cant seem to get it to work with the Propeller at all. The LCD works fine with my Stamps and in its test mode. I downloaded the code from column #134 of Nuts & Volts of BASIC Stamps, featuring Propeller Projects "Spin Baby Spin" which contains a demo for the BPI-216 with a custom object for it. Everything Ive read about the Propeller indicates that it should have no problem with a 5 volt serial LCD. I give it 5 volts and it works happily but does not respond at all to the lower voltage of the Prop. Also just for the record, yes I am powering the LCD with a separate 5 volt supply from the Props 3.3 volt supply its just the serial output from the Prop that the LCD isnt responding to. Thank you in advance for anybodies help.

Mike Green

Do you have the grounds for the Propeller and the separate 5V supply connected together? Are you using the Debug BPI-216 object from NV #134? The BPI-216 worked for Jon Williams. It should work for you too. Make sure that the Baud is set to 9600 on the BPI-216 or you'll have to modify Jon's object to use 2400 Baud.

gilabite

The main supply is a 5 volt and I have the Prop's 3.3 volt regulator running off of it, so the grounds are connected, is that wrong? Yep Im using the BPI-216_Demo from NV #134 with objects BPI-216_Demo.spin, Debug_BPI-216.spin, Simple_Serial.spin, Simple_Numbers.spin and BPI-216.spin with BPI-216_Demo as the top object. Yep the baud rate is set to 9600 on the BPI-216, I also tried 2400 on the LCD and code, but no go. I know it should be working.... its driving me nuts.

gilabite

Does anyone know what the differences between the versions of BPI-216's are? Mine is a v1.0 was wondering if that may have something to do with it.

gilabite

Well I finally got it to work. The only way I could get it going was to make an inverting buffer out of a transistor on the Prop's output. Dont recall seeing anything mentioned about that in NV#134. So Im wondering if there are some differences between the BPI-216's versions that was causing this. Anybody else have any ideas on this? One thing that Ive noticed and maybe someone can help me fix it, the LCD is getting turned on right away from the 5 volt on the inverting buffer and it keeps showing the test message before the Prop's program runs. The pullup resistor between the buffers output and the 5 volt is a 4.7k. I have a 10k resistor between the Prop's pin and the input to the buffer. Would adding a pulldown resistor after the 10k resistor stop the LCD from displaying the test message and if so whats a good value to use? Any other ideas to get it to stop would be appreciated.

JonnyMac

While I've never had any problems myself, things can get dicey with that display because Scott Edwards puts a current limiting resistor into the path of the serial line; this allows the device to connect right to a PC serial port which could swing up to +12v. The current limiter and pull-down form a divider that works great for 5v, but can be on the ragged edge with 3.3v.

My favorite unidirectional level translator is the (2-channel) TC4427. It's normally designed to drive MOSFETs but works well in many applications. It will accept the logic levels of the Propeller on the input side and the output is driven between ground and the Vdd of your choice. You could use 5v or 12v for the application where the output pin is going to the BPI-216. It's a nice, small (8-pin DIP or SOIC) that only needs a pull-up/down on the inputs and a cap across Vcc and ground.