TTL open level

A project log for Logic probe using ATTINY26

A Logic Probe with the usual LEDs and sound output based on an ATTINY26. My entry to the 1k challenge.

Klaus DormannKlaus Dormann 12/22/2016 at 13:210 Comments

just noticed that the input thresholds for TTL are not compatible with the resitor network on the probe pin. >= 2.0V is TTL high but the resistors source ~ 2.5V compatible with CMOS thresholds. One more resistor and an output pin of the ATTINY should do the trick.

update: The Problem was fixed by a redesign of the probe precharge resistor network and bypassing the resistor connected to Vcc in CMOS mode.