geekhack

geekhack Community => Keyboards => Topic started by: margo baggins on Wed, 19 June 2013, 13:41:48

Title: 38GT - Resistors - One final question
Post by: margo baggins on Wed, 19 June 2013, 13:41:48

Hello,

I am building a 38GT (not mine) - will 1N4148 diodes be alright?

Thanks

Title: Re: 38GT - Diodes?
Post by: danielucf on Wed, 19 June 2013, 15:45:38

Quote from: margo baggins on Wed, 19 June 2013, 13:41:48

Hello,

I am building a 38GT (not mine) - will 1N4148 diodes be alright?

Thanks

Those are the diodes GON told me he uses on his 38GTs so I think those will be fine.

Title: Re: 38GT - Diodes?
Post by: boost on Wed, 19 June 2013, 15:53:59

Those didoes will work fine.

Title: Re: 38GT - Diodes?
Post by: margo baggins on Wed, 19 June 2013, 15:56:16

awesome thanks for your responses  :)

Title: Re: 38GT - Resistors
Post by: margo baggins on Wed, 19 June 2013, 19:31:15

Excuse the double post - do you know which resistor I will need for the LEDs? They are SMD's but which are most suited?

Thanks :)

Title: Re: 38GT - Resistors
Post by: alaricljs on Wed, 19 June 2013, 20:04:40

http://ledcalc.com

It's LED specific in regard to how much resistance you need.

Title: Re: 38GT - Resistors
Post by: WhiteFireDragon on Thu, 20 June 2013, 01:39:35

Quote from: margo baggins on Wed, 19 June 2013, 19:31:15

Excuse the double post - do you know which resistor I will need for the LEDs? They are SMD's but which are most suited?

The size you want is 0805. Resistors for LEDs don't need very high tolerance values, so just pick the cheapest one. You can get thick film SMD resistors for less than a penny each if you buy 100.

The resistor value to choose will depend on voltage of the LED, like alaricljs said.

Title: Re: 38GT - Resistors
Post by: margo baggins on Thu, 20 June 2013, 04:06:25

hello, thanks for the replies - I know I need different resistance for different colours, 0805 was what I was after - thanks dudes! :)

Title: Re: 38GT - Resistors
Post by: margo baggins on Thu, 20 June 2013, 06:53:08

I'm getting really confused trying to work out these resistances.

The LEDs are wired in parallel on the board? I want to use white and red LED's that 3.3v and 2.4v respectively, 25mA would be fine. Can you offer any assistance?

Title: Re: 38GT - Resistors - One final question
Post by: dorkvader on Thu, 20 June 2013, 11:34:37

i'm not familiar with the board in question, but often, the LED's are wired between a 5V power "rail" and ground, each with a resistor in series with the LED for the purpose of current limiting.

If this is the case with your board, you should be able to use the calculator for a 5V source, and use that value resistor for them all.

Of course, I'd wait for another person with 38GT experience to chime in before committing to a value, but at least now they can quote this post and agree or disagree.

I could tell you for sure if I had a layout diagram, or even good pictures of both sides.