how to interface 5V LCD with 3.3V MCU

[prakashvenugopal]

Dear sir,

I had interfaced 5V LCD with 5V MCU. But now i have to interface 5V LCD with 3.3V MCU. MCU will tolerant upto 3.3V. I have to read the data from LCD. Will it damage the MCU?
If yes, what to do to interface 5V LCD with 3.3V MCU ?

Regards,
V. Prakash

 

[d@nny]

This question is also important for me.
i think use pull down resistances on data pins.

---------- Post added at 11:59 ---------- Previous post was at 11:57 ----------

LCD data pins are input only in write mode so dont worry

---------- Post added at 11:59 ---------- Previous post was at 11:59 ----------

but what about in read from lcd mode?

 

[prakashvenugopal]

pulling down resistor on data pin? How? when we read from LCD, it will have 5V on that data lines due to LCD 5V VCC?

 

[d@nny]

oh man why u r not connecting ur lcd with 3.3 volt rail
HD44780 datasheet page 48 topic DC characteristic
see the last line

 

[prakashvenugopal]

hi,

I am using the LCD LM16200. refer the datasheet attached. It has 5V Vcc.

 

[d@nny]

if u need to write data on lcd than it is not problem. but if u want to read also than i think pull down resistance could work . Another solution that i like and is proper to use 5v to 3v logic shift level as
74LCX245
Datasheet
https://www.fairchildsemi.com/ds/74/74LCX245.pdf

 

[alexan_e]

You can use mosfets (one in each line) as a bi-directional level shifter

d.holmes > hardware > simple bus level-shift
**broken link removed**

**broken link removed**


it is based on a Philips application note http://ics.nxp.com/support/documents/interface/pdf/an97055.pdf

Alex

 

[d@nny]

You can use mosfets (one in each line) as a bi-directional level shifter

d.holmes > hardware > simple bus level-shift
**broken link removed**

**broken link removed**


it is based on a Philips application note http://ics.nxp.com/support/documents/interface/pdf/an97055.pdf

Alex

what do u think can we use pull down resistances or 3.1v zener diode. We need to read and write from lcd i thnik the logic level for lcd and mcu can be maintain with pull down or zener?

 

[alexan_e]

the above circuit is all you need to READ AND WRITE, the gate is connected to the low voltage source , R1 and R2 work as a pullups.

when L1 becomes low the mosfet turns on and H1 becomes low too,
in the reverse direction if H1 gets grounded then L1 will become low too because of the mosfet diode

Alex

 

[d@nny]

the above circuit is all you need to READ AND WRITE, the gate is connected to the low voltage source , R1 and R2 work as a pullups.

when L1 becomes low the mosfet turns on and H1 becomes low too,
in the reverse direction if H1 gets grounded then L1 will become low too because of the mosfet diode

Alex

Is this available in single tube package?

---------- Post added at 13:14 ---------- Previous post was at 13:14 ----------

as the TTL draw much current i mean 74 series TTL

 

[alexan_e]

You can use any small Nmosfet as long as it has a low gate threshold to be able to work with 3.3v.
The mosfet used above is https://www.fairchildsemi.com/ds/BS/BSS138.pdf , you can buy it in single package

2N7002 should be fine too with 3.3v https://www.fairchildsemi.com/ds/2N/2N7000.pdf

 

[poorchava]

Wait a second. If i got it correctly from that datasheet no level shifting is needed. It states that input voltages is read as low from -0.3 to 0.6 V and as high from 2.2V to VCC (which is 5V for lcd). Output voltage is 2.4V for high and below 0.4 for low.

I guess that based on those informations you could try to interface MCU directly to the lcd. I just don't know if the output high voltage is exactly 2.4, or from 2.4 up to VCC. If that's the case u might need some resistor + 3V1 zener. On the other hand many 3.3V MCUs have 5V tolerant inputs. Maybe u can get one of that kind?

 

[d@nny]

74LCX245
Datasheet
https://www.fairchildsemi.com/ds/74/74LCX245.pdf
I think this is better choice for 8 bit mode and for 4 bit mode alex solution is best just 4 fets

 

[tsvetelin_velkov]

I would recommend this link :

https://www.ti.com/litv/pdf/scda006

hope this helps

 

[prakashvenugopal]

hi,

Thanks for the replies. I had already designed my board. Adding a mosfet will not be possible in that board. For the next development i will go for the mosfet pr level shifter. Now i can use the 3.3V Zener diode in the data lines (D0 to D7)?Please let me know.

Regards,
V. Prakash

 

[d@nny]

Try it?
It will not damadge your lcd or microcontroller as the voltages are 3.3v. So only one thing will be happened. That is
Working OR Fail
Try it and share it here for others

 

[nbb3i]

I have used LCD16x2 with dsPIC33 without any voltage buffer.
You can use 5VDC for LCD power, and 3.3V for MCU power. Data I/O can connect directly as the picture below.

 

[alexan_e]

Note in page 6 of the datasheet https://ww1.microchip.com/downloads/en/DeviceDoc/70265E.pdf
that only a few of the mcu pins are 5v tolerant



In your schematic
RS, R/W and E are connected to 5v tolerant pins but DB4,5,6,7 are not so if you try to read data from the LCD you will have problems

Alex

 

[nbb3i]

If you connect all pins of LCD Control and LCD Data to 5V tolerant pin, your design will be better. But I have tested and finished my design with schematic in pre. post. It's running well up to now (2 months)

 

[usufe]

Zener draws unnecessary current. As suggested earlier SN74LVC4245A works best.