full-featured double lab driver

[Zom-B]

I made a lab driver using the precision voltage to current converter I previously showed in this thread and which is remarkably similar to the author's.

It is designed with the following features:

• On/off switch
• Safety key switch with 8 seconds delay between safety switch turn on and laser power on. Laser power is physically inhibited by a relay. Output is also inhibited when the key is already turned on when turning main power on. (intelligence in microcontroller)
• Channel 1: 1-4V output, max current programmable between 250 and 500mA (red laser diodes)
• Channel 2: 4-7V output, max current programmable between 140 and 310mA (violet laser diodes)
• Each channel has a power adjust pot
• Each channel has a burst button which maxes out the supplied current when pressed.
• Each channel has an emission indicator with programmable threshold. They're a different color than any possible laser colors, as it should be visible through safety goggles.
• Each channel has an external safety interlock switch (which inhibits laser power when disconnected).
• Each channel has an external analog modulation input which overrules the internal pot automatically.
• Each channel has an on-time recorder v2 (big version), which can be read out using an external plug.
• One of the two channels can be switched off or both are enabled. (small 3-way switch between the two potmeters)
• Laser modules are connected using a common BNC connector. Each laser module must have it's own surge protection inside because of this.

(all images are clickable)


PCB Schematic (external components not shown, only connection points):



Work in progress:

This was an optional module from a Philips video recorder from 1984. It's use is unknown.




Harvested PCB with corner cut out and my own PCB mounted in it's place.

Plugs from top to bottom:

• Driver 1 output
• Driver 2 output
• Driver 1 interlock and modulation input
• Driver 2 interlock and modulation input
• Digital readouts for both on-time recorders.

The case I use is so ultra tight, I had to move some parts around on the PCB because front panel objects were in the way. Here are some photos showing how tight it is. Watch the switch poke upward while the caps (yellow blobs) poke downward.


Potmeter in lower front and heat sink from a voltage regulator in the center




Finished

The plug at the left is a dummy safety interlock switch

No, it's not upside down, I just need to make a good front panel layout

One recorder installed here on the lower right

 

[FrothyChimp]

Dude, I'm impressed! Yeah the driver is really neat but looking inside the driver I find someone who knows how lace. You don't see that anymore. I used to build class 5 telephone switches back in the day and everything was laced in. There were no plastic cable ties to be found anywhere. Lacing adds that extra bit of class to any project.

 

[Switch]

Wow , this is perfect as a PSU for modules in your scanner!

 

[Viracocha]

One thing i have wondered about this and other similar drivers is why would you have one opamp acting as the input of a second opamp? Wouldn't one be enough?

The drivers in the dx laser pointers used a similar system.

 

[Zom-B]

the left opamp acts as an impedance converter. The potmeter at the input is 100K Ohm, so if I would connect this directly to the resistor divider circuit (X2/R15/R12), the voltage would be divided amongst all potmeters and resistors, and control is lost. With the opamp, I effectively measure the voltage at the input and generate the same voltage at the output with enough current so that the divider circuit is accurate.

 

[Viracocha]

I think i get what you mean, but my electrical knowledge is still very limited. Thanks for the explanation

 

[lasersbee]

Nice build... I haven't seen wire lacing in more years than I care to remember...
We used to do that on Audio Mixers for the CBC studios up here.. IIRC..we used
waxed lacing chord..

 

[Zom-B]

While i was proudly showing my laser driver, everyone comments me on my lacing [smiley=dankk2.gif]. Though I didn't think it as something special. I even learned it at school (back in 1996) but forgot in the mean time. Now, my stitches aren't quite right and begin to get loose. The original purpose - to keep the wires in the same configuration from front to back - is also defeated by the chaos. The only purpose is to just keep them together so they don't go off swirling everywhere, blocking everything. The wires are all color-coded with no double colors, so there's no problem there either. I used waxed linen, which my dad had lying around for 25+ years

 

[Hemlock_Mike]

Frothy -- I haven't seen waxed lacing tape for 30+ years. That does bring back memories ;D

Mike

 

[rkcstr]

Pretty spiffy! I'm actually trying to make a few high power 405nm lab modules, but debating on whether I should make the driver one of these TTL/analog-type drivers or just constant-wave (which would be simpler).

I bet you could could make up nice small PCB for these, especially if there were any SMT equivalents for some of the parts (which would also simplify assembly).

You could either try to make a single small board with both drivers built-in, or make it modular so that you could set it up as a single driver or both, depending on your needs (would save on parts cost and space, if you don't need both drivers).

The place I just had some boards made through, Advanced Circuits (www.4pcb.com ), has some pretty good deals where you can get double-sided boards with hole plating, solder mask and silkscreening for $33 per 60sq in board (put multiple on one board), buy 4 get 1 free, so $133 plus S&H for 300 sq in of PCBs and they are in the US, so shipping isn't too expensive and you can actually get the boards pretty quick if you're in the US. If you're a college/grad student, you can order only 1 of the $33 boards, but it saves money to get the 5 for 4 price. Wish I could have mine that cheap, but that price is only good for standard thickness boards (0.064"). Anyway, let me know if you use them, though, as I can get referral bonuses

 

[Zom-B]

The driver with all gear attached:

 

[electron]

Wow that is some impression work you have done there, you must have put countless hour into it.