Hi, all!

I'm working on a for-fun project for a surgeon friend of mine. He trains residents in laparoscopic surgery and needs a way of directing his students where to cut/cauterize on an LCD video monitor, and his hands are already completely tied up with instruments. Therefore, I'm working on a head-mounted laser pointer controlled by a sip and puff switch.

I've got the sip and puff switch (World Magnetics was really nice to send me a free sample!), and I've got a green laser module (the DPSS-5) on order. According to the specs available, it runs off of 3V, and, assuming that it's a pretty typical module, it probably requires about 200 mA (based on other comparable lasers I saw).

The sip and puff switch is of the normally-open, momentary contact variety. I really need latched control of the laser, and I found the EDE2208 that seemed pretty good for that task. I know you can use T or JK flip-flops to do this, but this IC seemed much simpler (albeit 8x bigger than I really need) and has debouncing included.

This leads me to my next hurdle: I need to give the laser 3V and up to, say, 300 mA. I had planned on putting a 2:3 voltage divider on the 5V latched output of the EDE2208 to get a node at 3V wrt GND, and then put a buffer op-amp out of that node that could source 300 mA @ 3V directly to the laser. After several days of searching Digikey/Jameco/etc., I have not been able to find an op-amp that can do this.

Does anyone know of an op-amp that could be powered by a 9V battery that can source 300 mA? Also, I have thought about using a non-latching relay (5V coil voltage, no voltage divider needed)... should I go that route? I have also considered just putting three or four 100mA-capable op-amp buffers in parallel, but I've never tried it and don't even know if this would work. Any other project suggestions would also be greatly appreciated.

Thank you!

 

Take a look at National Semiconductors' LM134/LM234/LM334 series devices. They're 3-terminal current sources, and you can do a lot of things with them - plenty of application hints are in the docs. An ultra-simple current regulator can be made by using just the device and one external resistor.

Note that it has a temperature coefficient, which can be canceled out by adding another resistor and one diode.

Download the .PDF datasheet from either National or alldatasheet.com

 

Thanks for the input!

I just stumbled upon the Burr-Brown/TI REG104, which has an active-high enable pin that should be able to control power to the laser using the output of the EDE2208 (I think). I think I'll give this a try.

PS: Are there better/cheaper ways to get a basic 2-sided PCB made than by using ExpressPCB? I think that they charge $50 for three small boards.