wrong R20 value on Shruti-1 control board v0.7 ?
  • Hello,

    first of all, I must say I’ve been amazed the fast delivery (2 days only, I know I leave in Paris are, but this is still very fast) and the quality of the instructions provided for the SMR4 assembly, that I just finished.

    Now my question : the R20 resistor for the control board is 3.3ohm (orange,orange,black, silver,brown) vs 68 as indicated in the instructions. All the other resistors appear OK. Was there a change in the value ? If not, can I use a 43 ohm one (I’ve got a bunch of those in my stock) as a replacement?
    thanks in advance for your feedback,


  • R20 is the current limiting Resistor for the LCD. If Olivier provided another Value with the kit you can be shure that this matches the included LCD for maximum performance. If you are unsure you can always choose a higher volume but be prepared your Screen could be a bit dim. Are you shure its 3.3R (have you measured it)?. Sometimes the Colors are hard to identify.

  • You got one of the first “new generation” kits, which has green LEDs and a new type of LCD module. This new LCD module requires a very small current limiting resistor, 3.3Ω is thus fine.

    I’ll update the assembly instructions and silkscreen on the boards later.

  • Oh… Borg Style as in “Borg? Sounds sweedish”

  • thanks for the super fast answer ! I’ll then move forward, will keep you posted !

  • @fcd72: Hey, that’s offensive! Or something :) Darn Star Trek…

  • @Jojjelito
    At least one fellow Citizen of the ShruthiVersum™ spending his ever faster getting rare Lifespan with watching Epic TV shows…..

    I would anytime solder any component into anything pichenettes supposes.

  • @fcd72: As long as it’s some kind of sci-fi I’ll take a peek™ Our minister of finance is a Borg, at least in name. Damnit, there I was wanting it to be wrong, but no!

  • taxpaying is futile?

  • I have just built my first Shruthi today. It was a pleasure to build, and all seems to be fine, except…

    and it’s only a small except…

    I followed the assembly instructions on this site, but when it cane to the 68R resistor it seemed that the wrong component had been sent, so I went and found a 68R resistor and left the incorrectly supplied resistor to one side.

    So, of course, when I turned it on the screen seemed rather dim, and of course I put two and two together, then came here to the forum to check, and sure enough.

    So: two things.

    1) Please could you update the assembly instructions or enclose a note with the kit

    2) If something doesn’t add up, check on the forum to see if the answer is there (note to self)

    So, hopefully it should be a simple task to replace R20 – I haven’t looked yet, but I hope so!


  • I am sorry about this – I am sure I had written a note in the documentation but cannot find it now – I have fixed this!

    The most recent batch of kits come with green/yellow LCD modules which require a lower resistor than the nominal 68 ohm used for the white on blue LCDs.

    Note that you don’t need to desolder R20 if it’s hard to access – you can try to strap the 3.3ohm in parallel to it instead.

  • Thanks for the swift response.

    Yes, I thought it might be easier to solder a second resistor on top of the 68R.

    I shall give it a go once I’ve had my morning coffee :)


  • Done.

    I’ve soldered the supplied 3R3 resistor on the back of 68R and now have a lovely bright display.

    Now to make some noises.

  • Hi Oliver

    i just finished building my kit and the LCD is very dim . I have the blue grey black gold resistor for the LCD brightness . Do i have to replace it with a 3.3 ohm one? There isnt one in the kit , all i have left is 1 extra black black red red
  • What kind of LCD display do you have? Did your kit come with green or yellow LEDs?

  • Yellow LEDs I dont know what type of LCD as its very dim :(

    I can post a picture if that helps?

  • Actually , looking over my build and the instructions, I noticed I have the wrong trimpot on the LCD display , its looks the same as the trimpot for the filter board , except its labelled PV 36 5K , whereas the Filter Trimmer is PV36 20K , did I mix them up?

  • The trimmer for the LCD is used to adjust contrast. It won’t affect the backlight brightness.

    I’ve used different values before now, just means sometimes you don’t get the full range of adjustment for contrast.

  • But obviously if your filter board trimmer and LCD trimmer are mixed up then do swap them over :)

  • Yes, please send of photo.

    The filter board trimpot is 20k ; the control board trimpot is 5k. Which parts came with your kit and where did you solder them?

    If the LCD module in your kit is white on blue, it needs a 68 ohm current limiting resistor. If the LCD module in your kit is green on black, it needs a 3.3 ohm current limiting resistor. Kits sold before august had a white on blue LCD + yellow LEDs ; kits sold afterwards had a yellow/green LCD + green LEDs.

    The resistor adjusts the backlight intensity. The trimpot adjusts contrast. Before suspecting that it is a problem with the backlight or a wrong resistor, have you adjusted the contrast?

  • Thanks guys ,

    it appears to be white on blue, I did adjust the contrast and it makes it go from all faded squares then to faint digits, then nothing . here are the photos of the LCD in action and my shoddy soldering . HOLD ON! Looking at my photos it looks like 2 of the 1x16 pins for the LCD arent soldered correctly , I think I just tacked the middle 2 and forgot to go back afterwards , be right back!

    BTW I must say that the instructions were very straightforward and fun, I havent soldered anything like this ever and its been cool

  • Then your kit came with the right part ; 68 ohm is the required resistor value for the white on blue LCD and soldering a lower value might damage the display.

    Your problem might be related to the 2 unsoldered pins indeed…

  • KABOOM!!!! just like that, all fixed!

    thanks Oliver

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