DIY Laser Power Meter Interface Module

This is a companion thread to the DIY Laser Power Meter thread.

I've completed an initial design for a DIY Laser Power Meter RS-232 Interface Module and am attaching the schematic here.  This module uses a PIC12F683 microcontroller.  I'm using two of its 10-bit A/D inputs for two separate ranges: 0-1W with 1mW resolution, and 0-4W with 4mW resolution.  The overall design is simple.  The interface module accepts the output signal from the DIY LPM amp and splits it off to two separate amplifier channels.  To achieve 1mW resolution on the first channel, the signal is amplified with a gain of 5.  To achieve 4mW resolution on the other channel, the signal is amplified with a gain of 1.25.  The microcontroller converts both outputs simultaneously and streams both ranges out the serial port.  The host application will only need to pick the range it wants to monitor from the data stream. Optionally, the circuit can be configured for a single power range and a current measurement (0-1A @ 1mA res.) feature.

The Interface module can share the power supply (two 9V batteries) from the DIY Laser Power Meter.  I have a PCB design completed and if there is enough interest, I'll be offering this as a kit of parts.  I'll document the PCB/kit in an upcoming post.  

I'm working on a simple PC application to display power and export a log.  It will not be very sophisticated.  Regrettably, I will not be able to release the source code for my simple application because it uses libraries that are considered proprietary.  Ideally, someone else who's skilled in Visual Basic would come up with a more elaborate, open-source application for parsing the data stream and displaying/charting/logging laser power.  

This particular design has not been tested and I'll need to order PCBs and parts before doing so.  I'll be taking advance orders and donations to get this done.  I expect a kit of parts to be about $25.00 ea., shipped.

So who's interested?

Parts List

PCB information: I've designed a simple PCB for this project. The layout is attached below.

Group Buy PCBs will be ordered from Express PCB as a "MiniBoard". MiniBoard Service is their least expensive PCB option. The board size will be exactly 3.8 x 2.5 inches and the quantity ordered is always three. The boards have top and bottom copper layers with all holes plated through. They do not include soldermasks or silkscreen layers. Electrically, these boards are first rate with bright shiny tin/lead solder plated traces and pads. Because they do not have a green soldermask coating, the boards are the yellowish color of the industry standard FR-4 laminate. Three LPM interface circuits will fit on a MiniBoard so one order will yield nine PCBs.

The PCBs will only be sold as part of a kit. The kit will include the PCB, a programmed PIC, all the rest of the components listed in the BOM (above), an additional capacitor for the DIY LPM AMP mod, and instructions. The cost will be $25. per kit. When 9 kits are committed, I will order parts and PCBs.

(03/16/08)
Second Group Buy: (Kits shipped 4/7/08)

• Knimrod: 2 (paid)
• dar303: 1 (paid)
• Dark_Horse: 1 (paid)
• amkdeath: 1 (paid)
• Archane: 1 (paid)
• hologeek: 2 (paid)
• bluephoton: 1 (paid)
  
• Remaining: 0

(04/02/08)
Third Group Buy:

• membor02: 1
• 
  
• Remaining: 8

Version 1.3 of the LPM Interface Module Application available for download...

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man I was so excited about this, but is there a way to jus torder the PCB, and get the parts ourselves?

regards,

amk

I suppose but the microcontroller will need to be programmed and some of the resistors are 1%. I just thought it would be easier if it was a kit of parts.

knimrod said:

I suppose but the microcontroller will need to be programmed and some of the resistors are 1%.  I just thought it would be easier if it was a kit of parts.

Click to expand...

i see that is true. the 1% resistors are not a problem, but I am not in the mood to program any more micrcontrolers, the robotics competitions im in already have me booked.... mabe a discount or something? $25.... I dont know...

regards,

amk

Oh HELL YEAH....

I'll take a kit!!!!

That is a definate....just tell me how to pay..and when I can have it in my grubby hands!

Too Cool!!!

Larry

look at my PM

I'm in for 2 of these at least.

I'm in for 1 of these.

Looks like one piece of an automated test station.

you should also add a shunt and extra opamp to measure current, which would be useful in making curves

woop said:

you should also add a shunt and extra opamp to measure current, which would be useful in making curves

Click to expand...

Ugh.. Feature creep already..

There really isn't enough room for an additional op-amp circuit but what we could do is optionally eliminate the dual range power measurement feature and use the high range op-amp circuit for current measurement (0-1 amp @ 1mA res.).  How the PCB is populated and a single jumper installation would determine whether the current measurement feature is being used or not.  The only downside would be the loss of the high range (0-4W) measurement if the current measurement feature is used.  How's that?

(Schematic updated)

I think that is a good way to do it, not many of us will be using the higher range anyway and it would be really cool to do output/current diagrams for our different diode finds!

How will the PC side know if it is getting low range/high range or low range/current ?

dkelley said:

How will the PC side know if it is getting low range/high range or low range/current ?

Click to expand...

It'll have to be configured to understand the data stream.  In all cases the stream format will be the same.  It's just a matter of scaling the second parameter in the stream for 0-4W power or 0-1A current.