Home Built Laser Projector

Posted on Feb 6, 2014

This is the built servo amplifier and circuit diagram. This is a simple and ordinary op-amp circuit, there is nothing difficult. However it has power amplifier and small signal amplifier on the board together. You have to pay attention to unintentional coupling on board design otherwise you will be afflicted with oscillation, distortion or instability, and the servo gain will be limited. Currently the PD circuit is a little affected by power amplifier, it may be better to move it on the galvo like existing galvos. The servo amplifier requires a dual output power supply of ±20 volts. It is generated with a simple DC-DC converter powered from a single +12 volts DC supply. It is not that must be regulated, a traditional transformer-bridge-capacitor type power supply will also work well. This is a wave form which is a step response of the servo amplifier. It must be current controlled however the output voltage is saturating due to coil inductance. The supply voltage should be high as possible to minimize this effect. The voltage dip at high output current also be found. It is due to a current limiting of the LM675, a high power opamp, such as LM12, might be better than LM675. However such the strong opamp can burn the galvo coil with over load or oscillation so that any thermal protection will be needed to the galvo.

Home Built Laser Projector
Click here to download the full size of the above Circuit.

The laser controller must generate two vector signals (±1V analog) for galvos and a blanking signal (TTL) to modulate laser output, al least. These signals will able to be generated by any microcontroller board found in junk box or a simple D/A adapter attached to PC's parallel port. In this project, I designed and built a new controller board to minimize the board size. Figure 7 shows the block diagram for the controller board, and the circuit diagram is available in tech notes. The controller only generates vector data with stored frame and there is no more control. It will not needed to explain each function of the controller board and its firmware because you must have a skill to design a laser display controller if you are going to build galvos. Because the graphic data used in laser projector is vector based, not rastar based, generic graphic tools cannot be used to create frame data. Any vector based graphic tool is needed to create vector frames. There are some laser creation tools specified for vector graphics, but they are too expensive for hobby use or temporary project, so I developed a simple vector tracing tool. It handles the frame files in generic csv format because I also wish to use it for any other purpose :-). This is a freeware and is available in tech notes. A script to convert ild frame file into csv file is included too.

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