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Question : Problem: Electronics: LED flasher
I am looking to build an led flasher of sorts. (led hooked to a 74164). Problem is the 164 powers up w/ d0-d7 low and I don't want all leds on on startup-
| 164 |
|-------|------| DON'T want this
|
/\ led
|-------- r1---+5v
Thought your not suppose to drive LED's directly even though HCT devices can drive 20ma.
| 164 |
|-------|------| DON'T want this
|
\/ led
|-------- r1---gnd
thought about using:
| 164 |
|------|------|
|---r1---+5
\/ led
|--------gnd
when 164 powers on +5v goes thru r1 to 164 ground, led powers up off, Questions is what happens when 164 goes to 5v won't it go thru the LED. what the best (proper!) way to wire this??? wiring diagram + explanation would be great!
Answer : Problem: Electronics: LED flasher
TTL is ACTIVE LOW. You're only going to get the LED's to light in response to a 0 output. You want the LED's to come on in response to a 1, you're going to need inverter. 74x04/06/14 will all work. Check datasheets for drive limits, etc.
M
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