switch contact selection

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#1
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I have a low power project with three NO push-buttons and a SPDT toggle switch. Each contact is monitored through polling by ATtiny I/O pins with 1 meg-Ohm pull-down resistors, the 5V VCC is passed by the contacts. For the prototype I've thoughtfully selected switches with gold contacts rated at 0.4VA, but the selection and availability is very limited.

 

My question: Is it necessary to have gold contacts here?

 

The 5 µA is nearly nothing for the contacts, silver contact resistance of 10 or even a 100 Ohms shouldn't matter with 1 meg-Ohm pull-down resistors.

 

Stan

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I don't have experience on gold contacts x other...

But my concern is about your pull-down resistor and the 5 uA, noise can give false triggers depending of your pcb layout. How is the attiny pin configuration?

Regards,

Bruno Muswieck

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Noise doesn't seem to be an issue for this metal cased current loop transmitter project as the only switched lines are the five contacts noted above and a mechanical encoder having two 560k Ohm pull-up resistors. The largest possible transient is a 40µS step change of 19mA in loop current responding to the controlling DAC output, that current path being on the opposite end of the 5x9cm board from the ATtiny and controls. Only two leads enter the case, operating power is derived from the loop, limited to 2.8mA at 5V.

 

Stan

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Stan, I had never worked within such high resistor values but normally I avoid to use them.

Regards,

Bruno Muswieck