Author Topic: Adding a pull down resistor to a ttl laser board  (Read 559 times)

SteveK

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Adding a pull down resistor to a ttl laser board
« on: February 27, 2018, 03:22:48 AM »
I posted this in a new thread because I thought it might make it easier to find in a search. I want to be perfectly clear I understand exactly what to do. So I want to solder a resistor across the two pins I have circled on the TTL board? To my non electrical mind that seems it would cause a short. 

Steve

« Last Edit: February 27, 2018, 03:35:31 AM by SteveK »

ggallant571

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Re: Adding a pull down resistor to a ttl laser board
« Reply #1 on: February 27, 2018, 06:31:34 AM »
That is the place.

The resistor (2.2K to 4.7K) will try to bring the + signal to ground which is what you want in the non-active state. On RESET, the Arduino Nano waits about 2 seconds before it configures the signal as an output and drives it low. During this time the signal can float.

With the resistor installed it will not be able to drive as high but it will be sufficient to fully turn on the laser. The lower the resistor value the stronger its effect will be.
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SteveK

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Re: Adding a pull down resistor to a ttl laser board
« Reply #2 on: February 27, 2018, 07:12:41 AM »
Okay, I will get what I need ordered. Thanks again to you and Zax for all your help.

Steve

SteveK

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Re: Adding a pull down resistor to a ttl laser board
« Reply #3 on: February 27, 2018, 07:50:55 AM »
Okay, I am seeing 1/4watt and 1/2watt resistors, does it matter which I choose?

Steve

ggallant571

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Re: Adding a pull down resistor to a ttl laser board
« Reply #4 on: February 27, 2018, 09:53:03 AM »
1/8 would do. The amount of current (power dissipated) is negligible. The lower power resistor are physically smaller and the leads are thinner. If you want I will mail a few.
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SteveK

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Re: Adding a pull down resistor to a ttl laser board
« Reply #5 on: February 27, 2018, 02:03:25 PM »
1/8 would do. The amount of current (power dissipated) is negligible. The lower power resistor are physically smaller and the leads are thinner. If you want I will mail a few.

Sent you a pm

Steve

SteveK

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Re: Adding a pull down resistor to a ttl laser board
« Reply #6 on: March 03, 2018, 10:38:12 AM »
Sent you a pm

Steve

I received the resistors today. Still impressed by the generous offer and follow through. Busy weekend around here, probably won't get a chance to do anything with them til the middle of next week. Do I need to heat sink anything?

Steve