Reistor value for iPhone cable

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bratan
Posts: 16
Joined: Fri Jan 04, 2013 4:02 pm

Reistor value for iPhone cable

Post by bratan »

Quick question about iPhone adapter for Geiger Bot.
You are using 56K resistor. Would it work with other values such as 30K or 100K? I don't have any 56K resistors in my lab unfortunately :(

bratan
Posts: 16
Joined: Fri Jan 04, 2013 4:02 pm

Re: Reistor value for iPhone cable

Post by bratan »

Ok I did some more research, and it seems to me that you just need to bring voltage close to 50mV right? If I use voltage divider calculator correctly in your circuit you are getting Vout of about 53mV.
So if I use R1=10K and R2=200 I will get Vout=59mV. Would this work?
Tomorrow I'm getting iPhone cable, so I can test it with my iPad...

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mightyohm
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Re: Reistor value for iPhone cable

Post by mightyohm »

If you decrease all of the resistors you might need to adjust the size of C1 (bigger?)

I would try 100K for R1 and see what happens. Don't go much lower on R1 in case you overload and damage the mic input on your iPhone. You can also put resistors in series or parallel to make the 56K you need.

bratan
Posts: 16
Joined: Fri Jan 04, 2013 4:02 pm

Re: Reistor value for iPhone cable

Post by bratan »

Perhaps it was value of the C1... I couldn't get it working until I finally gave up and bought some 56K resistors. Now it works like a charm :)

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