Current limiting resistor for sparkfun LCD?

So I went and got the BW display from sparkfun, it needs 4.2 volts & 120 mA, am I right to think that a 6.8 ohm resistor should be about right?

Yes, looks right!

Thanks, also for future reference, the pcb is actually red, not green like on the picture at sparkfuns site, also it has the sparkfun logo so it appears as if they have them made.

damn that one looks good!

Newhaven white on black 763-0216K1Z-NSW-FBW seems to be very similar, consumes 10 times less current (68ohm resistor) and is available from Mouser for $11.90, I used it on 4PM and MidiBud, it looks very classy.

Echo @kvitekp, 120mA is an awful lot of current for a 16x2 display…

Could I blow the PSU?

Worst things that can happen:

  • 7805 getting very hot, especially if your input voltage is well above 7.5V.
  • Motorboating if your wallwart does not deliver enough current.

Nothing blowing up.

Olivier, how would a 7805SR work in these circumstances? I’m also thinking about the regulator in the Ambika which I guess is drawing a lot af current too (the cooling fin makes me suspect this). Would a 7805SR drop right in or would it require further modifications?

If you want lower temps and don’t mind spending €20 then they are fine. I use one on the Ambika as my VFD draws 0.3A peak.

They are overkill unless you have a high power demand or have a very warm climate.

hey i got a 6.8ohm instead of 68ohm resistor, can i still use this for the current limiting resistor for the LCD??

sorry i meant the resistor used for the brightness of the LCD. I have a newhaven Display that came with YME Shruthi semi kit.

Yes, indeed 6.8 ohm or less is recommended here.

cheers, that makes me happy. its nearly shruthi time