[sdiy] Juno 60 memory button carbon contacts

[Rutger Vlek]

Hi Tom,

I remeasured the resistances, and I now see they're much higher than 50R. More like 10 to 50K.  I must have been a little sleep-deprived during the first measurement.... Anyway, this rules out any problems in the circuit. It's behaving as it should. The carbon disks are just not shorting the contacts well enough to trigger the logic input on the uP.

Rutger



On 25 jun 2016, at 18:02, Tom Wiltshire wrote:

> 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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