>> Of course, when you buy a kit, somebody else has already figured out
>> what kind of LEDs to put in there, and what resister you need to connect
>> it to. I recall routinely using ICs to drive LEDs - but that was TTL,
>> and now I'm looking at CMOS, which has different characteristics.
> 
> Not that hard to figure out what kind of resistor you'd need to safely 
> drive an LED for a given voltage.

I wouldn't have thought so.

> You subtract the Vf of the LED from the supplied voltage, then use ohms 
> law to calculate the resistance you'll need to drive the LED in its 
> current range.

My plan was to just connect it up and see if it works - but sure, your 
way would work too. ;-)

> BTW, why CMOS? TTL is more robust for experimentation. CMOS you have to 
> worry about damage from ESD, etc...

This was my initial reaction too. However, it seems that CMOS has 
several advantages here:

1. It's fractionally cheaper.

2. It uses less power.

3. It has a much bigger fan-out.

4. It can source more current.

5. It works over a greater range of supply voltages.

Seems the only real disadvantage is static damage...

Post a reply to this message