USB Live Oscilloscope: Digital Input Board

Posted on Feb 5, 2014

The digital input board has 8 distinct digital inputs available on JP1. There are separate pull-down resistors (RN1, choose a value you like, e. g. 1MOhm) and then each input has a Schmitt-trigger. Since these may be destroyed by improper input voltages, I chose to use HC14 devices in DIL-14 packages and mount them on sockets to be easily replaceab

USB Live Oscilloscope: Digital Input Board
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le. Furthermore, one can switch from CMOS to TTL levels by plugging in a HCT14 instead or even have mixed inputs since there are two Schmitt-trigger IC`s, each one handling 4 inputs. The inputs operate on 5V or 3. 3V levels; for the latter, there is an on-board LDO (IC5) which generates the 3. 3V from 5V. This is not strictly necessary since we already have 3. 3V on the mainboard (available on the AD_DUMMY connector, actually. ), so you may choose to go for a simpler design. Note that when configuring for 3. 3V inputs, the digital bus voltage at pin1 on ADCV_DATA must be 3. 3V, otherwise 5V are supported as well (although we exclusively use 3. 3V for the USB Live Oscilloscope).

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