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Author Topic: TTL signal  (Read 3472 times)

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TTL signal
« on: January 04, 2011, 07:02:58 AM »
I am trying to set up my laser to do some wood burning. My laser driver requires a 5v signal to fire the TTL. I tested the voltage on pins 7(+5v), and one of my ground pins (18-25) and all I get is +2.8v to +3.0v. My laser is not coming on so I think this is the cause. Any suggestions?Thank You.

Offline Hood

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Re: TTL signal
« Reply #1 on: January 04, 2011, 07:53:06 AM »
Use a BOB that will take the 3v and put 5v out.
Hood
Re: TTL signal
« Reply #2 on: January 04, 2011, 07:58:55 AM »
You could make a small circuit using a schmitt trigger TTL chip supplied with a 5v source. This will give a clean output 0v-5v on-off for your laser.
Re: TTL signal
« Reply #3 on: January 04, 2011, 08:20:25 AM »
I would like to go with the small circuit due to the fact that I just bought a breakout board that does not have the 5v output. Is there a specific chip that you would recommend. I looked up schmitt trigger and found many variations of circuits, but not sure of the right one. I REALLY don't want to fry my computer in the process of figuring this out. Thanks again.
Re: TTL signal
« Reply #4 on: January 04, 2011, 08:47:28 AM »
Hi, TTL chip 7414. It has a few schmitt inverters each with an input and output. You will need to use 2 inverters in the chip, connect an output of one to the input of another. As each inverts the signal so by connecting two together means you original signal will be correct and not inverted.

The datasheet for the 7414 can be easily found online.

If connecting straight to a computer you really need an opto isolator too. If you already have a BOB, use an output on this and connect your new circuit.
Re: TTL signal
« Reply #5 on: January 08, 2011, 04:57:08 PM »
A real easy to configure solution for your tiny project board.

A simple PNP transistor will do just fine. ... wire the emitter to Plus 5 Volts, the collector to the laser input control, and the base to the port output through a 1000 ohm resistor. Also wire a 1000 ohm ohm resistor between the base and emitter to guarantee a clean turn-off

The transistor will pull to a firm VCC minus 0.3 volts.

Don't forget to set the turn on logic to low= ON

The transistor should be rated at about 100 ma collector current. The resistor values aren't critical and you could use values up to 10,000 ohms without consequence.

Good luck,
Bill

Offline Tweakie.CNC

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Re: TTL signal
« Reply #6 on: January 09, 2011, 07:00:02 AM »
I suggest using a buffered breakout board such as the C10 http://www.cnc4pc.com/Store/osc/product_info.php?cPath=33&products_id=45 which will accept your 3.3 Volt signals and output the required 5 Volts. There are other breakout boards with various characteristics and at various prices and they offer a neat solution to this problem.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.