I2C LCD driver board backlight voltage only 3V3 instead of 5V

TECHNICAL SUPPORT Sensors & Modules
1

Customer:

I found a problem with the I2C LCD adapter that seems to be causing the display to run slowly and with dim backlight. I tested another adapter I have and the LCD works fine. I suspect there’s a design flaw in your board.

On pins A and C for the backlight, the voltage should be 5V but I’m measuring 3V3. Your official pinout diagram also specifies 5V for these pins. The LCD datasheet also confirms it’s designed for 5V with an RF resistor of 91kohm.

Is there a way to modify the LCD breakout so I can get 5V on pins A and C?

Original message (Croatian)

Cini mi se da sam nasao problem zasto je Vas LCD display “spor” i

“slabo” backlight svijetli…

Problem je u Vasem I2C LCD adapteru…Probao sam drugi koji imam i

LCD je OK.

Pa si pregledajte da nije nekakav “design flaw”…

Naime, na pinovima “A” i “C” za backlight bi trebalo biti 5V a ja imam

3V3.

Cak i na Vasem sluzbenom pinoutu od breakouta pise da je 5V, slika u

prilogu.

A i u datasheetu od LCD displeja da je predvidjen za 5V i da ima “RF”

otpornik 91kohm, sto je tocno.

Jel ima kakav nacin da ja to nesto prespojim na LCD breakoutu da dobijem

5V na A i C pinovima?

Attachment omitted in migration: I2C-LCD-driver.png

Attachment omitted in migration: Soldered_20x4_lcd_datasheet.pdf

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Originally submitted via email support on 12 March 2024. Migrated to the forum for community visibility.

2

Soldered Support:

The 5V input is correct, and the 5V pin on the breakout measures 4.8V which is within tolerance. The voltage on pin A in the pinout diagram may be incorrect, but should be fine on the actual boards.

The board speed is limited by I2C data transfer, which is not very fast but is considered sufficient for most applications.

We’ll investigate further when we have time, but generally the breakout appears to be functioning correctly.

Original message (Croatian)

Hvala ti na detaljnoj prijavi za mogući design flaw. Šaljem u prilogu shemu za ovaj uređaj da ju možeš pregledati ako si zainteresiran. Na toj shemi možeš vidjeti kako postoje samo jumperi za izbor adrese i SDA i SCL pullup/pull down, što ne bi trebalo mijenjati svjetlinu ekrana.

Napon na ulazu od 5V je točan, i vidim da je 5V pin na breakout u 4.8 što je unutar tolerancije. Moguće je da je napon na A pinu krivi na pinoutu, a OK na samim pločicama.

Brzina pločice je ograničena s prijenosom podataka preko I2C-a, što nije baš pre brzo ali smatra se dovoljnim za većinu potreba.

Malo ćemo pogledati kad uhvatimo vremena, ali generalno mislim da je breakout OK.

Attachment omitted in migration: I2C LCD driver board Schematics.pdf

3

Customer:

Everything you said is correct, and I2C is what it is. However, the voltage on pins A and K for the backlight is not 5V when it should be. In your diagram I can see it’s measured at 3V. I noticed in the schematic that it goes through a MOSFET, so there might be a flaw there.

I’ll do some more investigating on the breakout myself.

Original message (Croatian)

Tocno je sve sto ste rekli, I2C je takav kakv jeste.

Ali napon na nozicama “A” i “K” za backlight nije 5V, a trebao bi

biti…Na slici ste vidjeli da je tu izmjereno 3V.

To u shemi vidim da ide preko nekog MOSFET-a, pa da nije tu kakav

“flaw”.

Jos cu i ja malo “pronjuskati” po breakout-u.

Hvala !

4

Customer:

The schematic shows R5 as zero ohms, but in reality it’s 330 ohms. I removed it and now I get 5V on pin K.

Original message (Croatian)

Eh, u shemi pise da je R5 nula ohma-a, a u stvarnosti je 330 ohm-a :slight_smile:

Skidam ga, i dobijem 5V na “K” nozici :slight_smile:

5

Soldered Support:

Thank you for reporting this. I’ve passed this to our R&D team and they’ve confirmed it’s been fixed in a newer version. Here’s what I found:

“In the previous version V1.1.1, we had a 330R resistor on the schematic and it was placed on the board. In the new version V1.2.2, we have 0R.”

So this issue has already been resolved by R&D. Version V1.2.2 is being manufactured and should be arriving in stock soon.

Original message (Croatian)

hvala što si javio, poslao sam ovo našem timu za R&D i rekli su da je ispravljeno u novijoj verziji proizvoda. Evo što sam saznao:
“U prethodnoj verziji smo V1.1.1 smo imali otpornik 330R na shemi i to je stavljeno na pločicu. Na novoj verziji V1.2.2 imamo 0R”.

Tako da, izgleda da je već riješeno od strane R&D-ja. V1.2.2 se tek treba proizvesti i doći na stanje.