Square wave generator tool (DPSS adjustment)

[MIIKKKLLLL]

Hello everyone,


I had an idea a few time ago : build a simple and user friendly square wave generator tool at low costs. As direct green laser diodes don't worth it for a medium to high power projector in 2013 (personal opinion ), the use of green DPSS laser is still interesting.

Good DPSS are composed of several parts including some cooled parts. These areas include temperature sensors. Then a few potentiometers located on the driver are used to adjust the PID response for the management of the TECs.

The usual steps for adjusting a DPSS is to send a square shaped signal with a duty cycle between 70 and 80% and then adjust the potentiometers to get maximum output power in "REAL CONDITION" use (and not CW, the vast majority of DPSS are adujsted like that !). To do this there are several solutions: start the computer and use a software + DAC and generate a frame having a characteristic proper duty cycle (waste of time...), and then opt for scientific equipment : a wave generator which is in most cases very expensive.


As I had a useless small box of aluminum and spare parts, I only had to buy the generator itself for the price of €3 including FDP : http://www.ebay.com/itm/NE555-Duty-Cycl ... 1e79cbf4b8

The advantage of this generator based on a NE555 compared to many other more expensive models is that we can adjust the duty cycle AND frequency. I also added a knob for tension adjustment.

Some technical data of the case:

- Compact design, no external power supply needed
- Powered by a 9V battery
- Voltage adjustable 0-8V
- Adjustable Frequency from 0.4Hz to 0.5MHz
- Adjustable duty-cycle from 5% to 99%
- Integrated voltmeter to indicate voltage
- Selection of frequency ranges with a 5 positions knob
- Output selection via rotary 4-way knob (blanking, green, red, blue)
- LED indicator showing the output frequency (only useful for f < 30Hz )
- Compatible with standard connector DB25 and ILDA
- Output connectors to adjust the frequency and duty cycle with an oscilloscope or an advanced voltmeter

Some pics (early afternoon, with the case still open and cables not 100% wired):








Adjusted at f=8kHz, 80% duty-cycle:




Then you just need to put a watt-meter at the laser output and compare the results
Attachment 38771


Cheers, Mike