Electronics: LED flasher

Posted on 1998-10-23
Last Modified: 2012-08-13
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    |  
       \/ led

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!
Question by:bculver
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2

Author Comment

ID: 1127543
Edited text of question
LVL 11

Expert Comment

ID: 1127544
*smiling* hard to read your diagram, wish they allowed non-prop text here, i think from how i see it, you need another resistor  in series with the LED, 220 0r 330 ohms should do *smile*


Road Warrior
LVL 12

Expert Comment

ID: 1127545
Stick an inverter (7404) on the output of the counter. Tie the LED to the +5 rail via a resistor. Figure for 10mA or about 330 ohms. TTL logic *sinks* current rather than sources current. Thus trying to use the high state to feed an LED to ground generally won't work. The low state can sink about 20mA, but if you drive *all* to 20mA you'll overheat as you'll exceed total draw.



Author Comment

ID: 1127546
mark2150: Was not looking to add extra active parts (IC's). Passive components ok (resistors etc.). If inverting the output with ic's is the only answer, let me know and i'll give you the points anyways. Thanks.

RoadWarrior: Glad you liked my schematics! A pictures worth a thousand words right?:}
 I believe that adding a resistor in series with the led brings me back to the original problem of driving the led with the IC. thanks though!
LVL 12

Accepted Solution

mark2150 earned 50 total points
ID: 1127547
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.


Featured Post

Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Issues cloning my HDD to SSD 12 126
server room temperature control 24 106
Samsung Tablette 22 101
Web Cam for Skype 1 38
Monitor input from a computer is usually nothing special.  In this instance it prevented anyone from using the computer.  This was a preconfiguration that didn't work.
This article outlines why you need to choose a backup solution that protects your entire environment – including your VMware ESXi and Microsoft Hyper-V virtualization hosts – not just your virtual machines.
This video teaches viewers how to process images for a time-lapse video. Programs required: Adobe Lightroom, Adobe After Effects, Video Editing Program. In Adobe Lightroom: Import sequence image files into Adobe Lightroom: Develop settings of an I…
Suggested Courses

752 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question