Can someone explain TTL to me?

[mhein68]

I have been reading my paperwork and have came across several references to TTL- Level Control Signal... I searched the internet but haven't came across a plain idea as to what TTL is... If someone is game to try explaining in simple terms I'm listening.. What devices use TTL? How would I Use it in the future? Thanks! ???

[tds234]

Wikipedia is a good source http://en.wikipedia.org/wiki/Transistor%E2%80%93transistor_logic.
Especially read the theory section but essentially low voltage (5V reference) and very low current draw versus hooking up something to the prop-1 that draws a lot a current like a motor or solenoid which is not at TTL levels.
Mainly keep in mind that CMOS/TTL, and such are logic level circuitry not intended for macro scale stuff like motors, solenoids, lights. Other TTL devices will be logic gates, or other 'chips' that are intended for computation mostly.

Doug

[menehune]

Yes, TTL is basically for microcomputer and processor "internals" and not really designed to interface to the outside world.  A computer needs to convert the TTL levels (0-5Vdc) to something outside circuits can use-typically RS232 serial. 

RS232 interfaces use different voltage levels for signaling so the interfaces are not exactly equivalent.  That is why you need RS232 drivers (and the BS1 serial adaptor) for a microprocessor to talk to your PC.

You might use TTL circuits with a Prop2 (or Prop-SX) to interface memory chips, Real time clock modules , temperature sensors, light sensors, switch closures, GPS units.  The Prop1 is a "simpler" processor so you may use TTL circuits for rheostats (speed control), switch closures, driving small hobby servos.

[mhein68]

Thanks everyone for the explanations... I am slowly learning.. Thanks!