[sdiy] Juno 60 memory button carbon contacts

Tom Wiltshire tom at electricdruid.net
Sat Jun 25 18:02:39 CEST 2016


That's weird. 33K/50R across 5V gives 7mV, so that's *way* below any logic threshold.

Something else must be going on. Can you trigger the non-working switches "manually" by shorting the contacts on the PCB? Can you trigger them shorting them with a 100R resistor?

Regards,
Tom

On 25 Jun 2016, at 16:44, Rutger Vlek <rutgervlek at gmail.com> wrote:

> It's a diode switch matrix with a resistor array of 33K pull-up resistors (to +5V). The matrix is scanned directly by the CPU. I don't see any correlation with specific lines (rows or columns) of the switch matrix being problematic.
> 
> Rutger
> 
> 
> On 25 jun 2016, at 15:38, MTG wrote:
> 
>> Maybe there is a secondary problem for those? What is the circuitry that drives or senses the contact?
>> 
>> On 6/25/2016 3:00 AM, Rutger Vlek wrote:
>>> 
>>> Personally, I'm surprised 50 ohms is not low enough to trigger the detection of a closed switch.
>>> 
>>> Regards,
>>> 
>>> Rutger
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