Is the LCD117 able to receive 3.3V logic signals?

Interfacing hardware, sensors, output drivers, chips.
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jhornbr225
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Joined: Tue Dec 23, 2008 8:20 pm

Is the LCD117 able to receive 3.3V logic signals?

Post by jhornbr225 » Mon Jan 09, 2017 12:54 pm

I'd like to use an older, through hole LCD117 to display messages from an ESP8266. Seeing that the ESP8266 is 3.3V only, will the LCD117 accept and display Serial print commands at 3.3V?

I'm assuming that I'll still have to power it with 5V, which is fine. I have 5V available, I then use a regulator to get 3.3 for the ESP8266.

So I use a 5V display, hook 5V and G of the LCD117 to the 5V supply, and hook Rx of the LCD117 to the output pin of the 8266.

Will that work and not damage anything?

Thanks,

JHornbr225

paul
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Re: Is the LCD117 able to receive 3.3V logic signals?

Post by paul » Tue Jan 10, 2017 11:02 pm

JHornbr225,

I believe we tested the LCD117 at 3.3V and it ran fine.
You would need a 3.3V LCD - which we have in the shop BTW.
Most of them are pretty flaky at low voltage.

Paul

jhornbr225
Posts: 7
Joined: Tue Dec 23, 2008 8:20 pm

Re: Is the LCD117 able to receive 3.3V logic signals?

Post by jhornbr225 » Wed Jan 11, 2017 7:51 pm

I already have a 5V LCD, and I am using a 5V supply. Can I run the 3.3V TX off my 8266 into the RX on the serial backpack and have it work?

So the three pins on the Serial Backpack:

G - Ground
5V - 5V Power Supply
RX - 3.3V signals from 8266

#1 - Will it work properly? Is the 3.3V enough to be considered a "High" level?
#2 - Will it damage anything?

paul
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Re: Is the LCD117 able to receive 3.3V logic signals?

Post by paul » Thu Jan 12, 2017 10:06 am

#1 - Will it work properly? Is the 3.3V enough to be considered a "High" level?
Yes - as long as 3.3V is solid - I think it will work fine.

There are also some things to try if this turns out to be problematic, such as a level shift chip.

#2 - Will it damage anything?
No

Good luck with it.

Paul

jhornbr225
Posts: 7
Joined: Tue Dec 23, 2008 8:20 pm

Re: Is the LCD117 able to receive 3.3V logic signals?

Post by jhornbr225 » Sat Jan 14, 2017 4:48 pm

I did move forward and use a NPN transistor level shifter with the 3.3V output from the 8266 going to the emitter and the collector going to the 5V Rx on the LCD117.

Now another question. I see in the documentation of the LCD117 and the code examples that there are outputs on the LCD117. I see there is also a buzzer. Are those outputs available to me?

I see there are 3 plated through holes in the board next to pins 10, 11, and 12. I found a pdf of a hand written document from www.phanderson.com that shows 10, 11, 12 and 13 are outputs 4-7. On an ESP8266-01 with technically only 2 IO pins, 4 extra outputs would be very handy. Is there an easy way to access these outputs from the Serial Backpack?

For outputs 4, 5 and 6 I think I could just solder a wire into the plated hole next to pins 10, 11, and 12 on the chip. I'm not sure what I could do about output 7 and the buzzer. It looks like maybe those pins are unused (not tied to anything on the board). In that case, I could just solder a wire to the socket's pin on the bottom of the board. Was that the intention in the design of the board?

Thanks for the responses Paul!

paul
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Re: Is the LCD117 able to receive 3.3V logic signals?

Post by paul » Sun Jan 15, 2017 12:42 pm

jhornbr225,

Unfortunately I don't think we brought out a connection for the buzzer pin - the docs say pin 6 but I think I remember that this is PIC pin 6. You could code the buzzer in a tight loop then use a small speak in series with an electrolytic cap to probe the pins with - to quickly locate the buzzer pin. If your really want to use it you would wire solder the cap to the dip pin on the chip if you're using the DIP version. The SMD version would require a bit more skill to tag a small wire onto the pin. All-in-all probably a job for your main uC.

The other pins are accessible from the Phanderson code using:

?H High output on auxiliary digital pins: valid
numbers are 4,5,6
Serial.print("?H4");
// aux pin 4 HIGH

?L Low output on auxiliary digital pins: valid
numbers are 4,5,6
Serial.print("?L4");

jhornbr225
Posts: 7
Joined: Tue Dec 23, 2008 8:20 pm

Re: Is the LCD117 able to receive 3.3V logic signals?

Post by jhornbr225 » Tue Jan 17, 2017 3:40 pm

I see that the buzzer pin might be more problem than it's worth. I'll probably use a piezo unit anyway, not a speaker.

Do the PIC pins correspond to the pins on the DIP chip?

i see 4, 5, and 6 on the silkscreen, but can't seem to find 7. Is it not labeled on the board? Or would I have to take that directly off of the PIC pin? Output 7 looks to be pin 13, can you confirm?

Is there a schematic available?

paul
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Re: Is the LCD117 able to receive 3.3V logic signals?

Post by paul » Tue Jan 24, 2017 4:01 pm

The LCD 117 SMD version has a schematic.
I believe I designed the LCD117 from a hand drawn schematic of Peter Anderson.

Brian Riley at Wulfden has a similar but not completely identical. The schematic may be found here
wulfden.org/downloads/manuals/K107manual.pdf

Pin 13 is PB7

paul
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Re: Is the LCD117 able to receive 3.3V logic signals?

Post by paul » Sat Feb 04, 2017 5:29 pm

jhornbr225,

The 3.3V signal won't hurt anything. It should work fine if you power from 5V. If you power from 3.3V then there it may or may not work depending on the generation of chip in the LCD117.
Make sure you use a 3.3V LCD or you won't know if the LCD117 is working.

Paul

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