Trying to wire up some stuff using TTL chips on a breadboard...

[JohnCU]

I know these are supposed to use 5 volts, but all I have is a 4.5V source...and my chips are acting weird. Like the 7408 AND is producing an output when only one of the two inputs is high and the other is low...is the problem my lower voltage?

I don't really see how having a difference of .5V could affect them, but I'm fairly inexperienced.

 

[JohnCU]

Well, on further investigation, if I wire one of the inputs of the AND to the ground, and one of the inputs to the 4.5v, it performs correctly, but if no wire is connected to the other input, I get a logic 1 produced.

 

[Cruisin1]

Is this an LS part? Please be more specific on the chip part (I'm assuming LS since you said TTL). If that is the case thatn 5V source will work fine, you should read the data sheet. It will have an operating voltage range, that is usually an entire volt (ie. 4.5 - 5.5V).

 

[DAM]

the .5 V might be making a different in your ckt, also ensure that everything is grounded to a common source.



dam()

 

[agnitrate]

Check the data sheet. 4.5V might be a problem depending on the part. Are you sure the chip is properly grounded?

-silver

 

[TheLonelyPhoenix]

Just about all ICs treat anything between 4 and 5 volts as a logic 1.

Make sure you're really getting a logic 0 input. The "wired OR" gate is fairly common among beginners: caused when you just connect two wires together instead of using an OR gate. Because IC circuits aren't perfect, there may still be some current in each wire in a wired OR, thus inducing a logic level 1 when it should be 0.