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Old 08-29-2017, 03:40 AM   Thread Starter #1
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Default How to Attach Drum Pad to ADC0802

I'm a bit of newbie in the electronic area, so if this question has an obvious answer, please excuse me.

I am trying to attach an electronic drum pad to the Vin input of an flash ADC--ADC0820 . I am powering it with 5 V and using a 3.3 V reference voltage (the voltage ref is a differential input on this IC, with a VREF- of 0 V.) When I attach a 10 k pot to the ADC VIN input, everything works as expected.
ADC0802 Datasheet
Here's the thing that's confusing me: when I hook up a scope and read the drum pad when it's not attached to the ADC, it reads at 0 V when not being hit. However, when I attach it to the VIN input this level rises to 0.1 V and causes the ADC to read above 0. This doesn't happen when I experiment with different ADC chips.
OH! Right! It seems the VIN pin is charged from the VREF+ pin and this is being sent back down the drum pad. I have confirmed this by connecting a pot to the VREF+ pin and turning it up and down - the charge leaving the VIN pin changes!
Why is it happening here?
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