PWM control

Hi people,

I have an 1992 Synrad laser. I need a PWM controller to set the intensity. I'd like something that has an input that can be controlled by a pin on the Parallel port of a computer, but will be happy with a manual control that I can set for intensity.

Because the laser is so old Synrad no longer has any info on it. I have made it burn stuff by using a AA battery on the intensity line so II know it is working now.

I am retired and on a tight budget but thought I may be able to use this to engrave stuff and a make a few bucks on the side. It was given to me because the laser was dead, but I now have it working albeit at only one output level.

Synrad did say it was controlled by a PWM signal. From their controller manual...

1us tickle pulse at all times to keep the laser on the verge of lasing. Output voltage is 0-5vdc. Output current 100ma through a 50ohm CMOS driver I get the impression that anything above a 2us pulse will drive the laser on.

Can anyone assist me here with a kit or schematic or something, anything?

Thanks in advance.

Dave

Reply to
Dave, I can't do that
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Forgot to mention it is a 5kHz signal

Dave

Reply to
Dave, I can't do that

Should be pretty easy. How do you want to go about it? Are you used to programming uC or soldering chips?

One easy way might be to use a 555 timer? There are many kits and schematics available. You can get individual PWM chips too. Its very simple to implement it in a uC. If your willing to spend 30-40 bucks on the Pickit2 I can send you some code that will take the input of a pot and output a corresponding PWM. (it needs to be the pic24's though)

The PicKit2 lets you program pic's pretty easily by just writing code(download free MPLAB), and burn it. You can even debug them and it can act as a logic analyzer(not used that yet). So its a pretty decent investment if you plan on messing around with this kinda stuff.

Reply to
Jon Slaughter

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See page 5: The first circuit is an astable that puts out your 5 KHz; you'd want to differentiate its output (output to 1-10 nF cap, other end of cap goes thru 10K resistor to ground AND to trigger of the monostable. Design the monostable for a pulse width of 1.0 uS to as long as you want.

Use that to drive the PWM input, with the appropriate driver.

Good Luck! Rich

Reply to
Rich Grise

Hi Jon,

Thanks for the reply.

Let me answer that by saying I am a retired mechanical engineer. I have built many electronic kits over the years and to the best of my memory they have always worked firs time, so I guess I am OK with soldering.

While I am not averse to investment, in this instant it would be doubtful if I would ever use the programming stuff again. I would prefer to get a kit or schematic with board layouts.

All of the kits (except Velleman, none in stock that I have found yet) that I have found so far are 12vdc and up. Since the laser is a costly part of the project and I lucked out on getting it working, I want to approach it very carefully and the 5vdc and 100mA max are paramount for whatever I use.

Dave

Reply to
Dave, I can't do that

Hi Rich,

Waaaaaaay out of my area of expertise to design something. Thanks.

Dave

Reply to
Dave, I can't do that

Aw, come on, Dave - it's already designed! All you have to do is solder the parts together. Of course, you'd need to use the chart to get your R and C values, to give you the right pulse width and interval, but that's only arithmetic.

Or, you might be able to swindle someone here into giving you a full design and layout, but at 5 KHz it'd be a great beginner-level project.

In any case, good luck!

Cheers! Rich

Reply to
Rich Grise

Thanks Rich,

The Math will be fine, but this also has to be adjustable for varying the laser intensity and it is at that point it starts to get complex for my abilities in electronics.

Dave

Reply to
Dave, I can't do that

It's sounding like this would be more appropriate on sci.electronics.basics ; You're more likely to get some help over there, since it's intended more for beginners; somebody might even slap together a schematic for you.

Good Luck! Rich

Reply to
Rich Grise

I've used a dual op-amp set up where one op-amp act's as the triangle wave generator and the other the voltage comparator for the pulse width.

Something there you can look at..

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I suppose the bulb could be replaced with the laser unit for the low side :)

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Reply to
Jamie

Thanks Jamie, I will see what parts I can get from the local RS store.

Dave

Reply to
Dave, I can't do that

Thanks Rich, I will try there.

Dave

Reply to
Dave, I can't do that

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