Hey guys, was looking for a logic probe shematic and came across this: http://www.electronics-lab.com/projects/test/020/index.html Been trying to figure out how it works... I dont understand how the high LED lights when the test signal is high as the 74ls00 can only sink 8 ma? Even if the second NAND gate assisted by sinking curent the Iih is only 20uA? Also whats the point of the pull down restor to earth on the bottom input of the left most NAND gate? Thanks guys!