Logic probe by iainhendry January 31, 2015 1.4k A logic probe using a 555 timer a 74HC00 and some other components Schematic logic probe Logic Probe 0 FacebookTwitterPinterestEmail previous post TTL device types next post TDA2003 10W audio amplifier You may also like Battery Low Voltage Indicator January 2, 2014 Logic Probe December 19, 2013 square wave oscillator December 19, 2013