Mobile Laser/Light Controller PC

The front panel
The back panel
Construction
The old PC

I got an old pentium 166MHz from a friend and have decided to build it into a box. The purpose of the PC is to be that of a mobile PC which will be used for my laser and lights. Additionally I also intend to use it for on site audio recording, as well as to take the PC to a site to reprogram microcontrollers.

I have removed the CRT monitor's insides from its case and mounted it in my own box. The same goes for the PC itself and also the amplified speakers. I have also added additional circuits including an audio router panel, a variable output power supply to power external device programmers, and the laser and light control circuits.

If I have the option of using new components, I will definitely use a LCD screen, CRTs are large and can be dangerous if it is damaged. Furthermore it is heavy and magnetic fields from transformers of nearby equipment causes interference. I don't think I will go to a laptop. Although a laptop itself is compact, the laptop still needs to be connected to peripheral devices to do what this PC can do, which can lead to an untidy mess. With this PC everything needed is build in, and things can easily be added.

Building a PC like this is not that simple, especially concerning the CRT monitor. A CRT is a very dangerous device since if handled incorrectly it may implode. Furthermore it should be mounted firmly onto a frame, which should not put any stress on the CRT, even if external pressure is put on the frame. There are also high voltages present in the monitor circuit, the 25kV needed for the monitor anode being one of the least concerns, since the output current is very low. The more dangerous voltages are present in the power supply circuit on the PCB. Even after the monitor is switched off and disconnected, the power supply filter capacitor may still be charged with a voltage of 300V or more.

Below is a front view of the PC:
   



The front panel:

Below are close-ups of the panels. The first one is the one right below the screen.

 

This panel is used for the monitor's controls as well as for the indicators and buttons of the PC.  Below are the two panels to the left and to the right of the screen.



The left panel contains the power switch, headphone output as well as the voltage control for the built-in variable output power supply. The purpose of the variable power supply is to supply power to the microcontroller programmer, or any other device which is connected to the PC. The output of the power supply is available on the back panel. The right panel contains the audio controls. The unit has built-in speakers, which is automatically disconnected if headphones are plugged in. At the top-left is the PC speaker control. The switch switches the physical speaker on or off, while the level control controls how loud the PC speaker is heard over the stereo speakers/headphones. The next level control controls the volume of the stereo speakers. The rightmost level control controls the level of the audio output on the back panel. In the middle is the laser and light controls. Audio may be sent directly to the laser's X and Y servos. The ASSIGN switch selects whether the audio comes directly from the back panel, or if it comes from the output of the sound card. The two SIZE controls controls the amount of audio send to the servos. The MUTE switch is used to mute all the light outputs on the back panel. Below are two auxiliary outputs which, just as with the laser, my be tapped from either the back panel input or the sound card output. The LEVEL controls control the level of the auxiliary outputs on the back panel.

 
The  back panel
 
Below is a photo of the backside of the PC. There are two connector panels, one for the audio and lights connectors and one for the PC's serial and parallel ports. The box also has two extractor fans, one inside the power supply as well as an additional one.


 
  Below are close-ups of the two connector panels.

 

The above panel is used for all audio and light connections. The system has 4 8-channel port outputs. Each of the 4 8-channel ports is available on a DB9 connector. The first 5 bits is also available on a 5 pin DIN plug. The remaining outputs of the first two ports are used to control 4 strobe light's as well as 2 smoke machines. The Smoke machine ports also reads in the status of the machine ready indicator. All these outouts are eiter on or off. The MIDI ports from the sound card is also available on the backplane. There is also a MIDI thru port. There are also three connectors (HDM1-3) for my own in-ear monitoring system. The laser control output is the topmost connector on the right. Below this is the audio input and outputs. Below is a photo of the computer connector panel:



The computer connector panel is used for the computer's serial and parallel ports. There are two parallel ports (LPT1,2) and three serial ports (COM2-4). COM1 is used internally for the mouse. The output terminals of the variable voltage PSU is also placed on this panel.

Construction

Below are photo's showing the PC in various stages of construction. The first photo shows the basic frame. I have constructed the frame using aluminium angle irons (25mm x 25mm x 1.6mm). I used M4 screws to fasten everything. I have put glue on the nuts which will never be removed. This is important since if a nut and its washer comes loose, it might fall on the electronics and cause a short circuit. 


 
Below are a front and rear view of the partially constructed PC.

 
 
I have removed the monitor from its housing and have mounted the CRT and electronics on the aluminium frame. I have moved the monitor's LED's, switches and brightness and contrast pots onto a piece of Veroboard which is mounted just below the CRT. For safety reasons, I put a carton beneath the monitor's PCB. I glued aluminium foil to the underside of the carton, which is in electrical contact with the aluminium frame. The is to shield any electrical noise generated by the monitor electronics, as well as to cover the high voltages present on the bottom of the monitor's PCB. I kept the motherboard on the baseplate from the original PC case. The CDROM, harddrive and stiffy drive was also kept in the original mounting frame from the PC case. Below is a front view of the PC at a later stage in its construction.


 
Here the top and bottom hardboard panels of the box is mounted, as well as some other panels. I have used PCB's for the front panels, it is relatively easy to drill and file it, and I had a lot of surplus PCB lying around which I bought for cheap. Below are sideviews of the left side of the unit at various stages of construction:

 
The PC power supply is mounted directly onto the back panel. The PCB to the right of the power supply is the amplifier board for the PC speakers. I have used a lot of cable ties to make sure that there are no loose wires. Below are side views of the right side of the unit at various stages of construction:


 
  The power supply for audio circuits are mounted on the aluminium plate in the center. The smaller transformer is the transformer for the speakers. As can be seen, the aluminium plate was moved to the back of the box. The magnetic fields of the transformers caused interference on the CRT image. Moving the transformers to the back wasn't that effective. In the end I changed to wiring on the transformers so that the two are fed out of phase. Since the two generated magnetic fields now cancels each other, there are no longer any interference on the CRT image. The PCB which can be seen at the bottom right of the second image is the laser controller digital to analogue converter card.

I used hardboard for all the sides of the box. I used thin plywood to make the odly shaped panels around the monitor and the diskdrives. I have found that is is very easy to cut plywood with a knife, must easier than cutting hardboard. I have so far used plywood for several PC frontpanels.

The old PC

Here are some photos of the first portable PC I build. I have used it a lot in the field as a portable PC, but since I have the new PC now, I have disassembled this PC. This one was based around a 486DX2-80. Here the monitor was not build into the box. There is a space above the stiffy drive to hold the mouse, a mousepad which slides out, as well as a light to illuminate the keyboard in a dark room.



Here I used wood as construction material, the motherboard was also directly mounted onto the bottom of the case. Luckily the wooden case was strong and it didn't flex, which can seriously damage the motherboard.  Below is a photo of the inside of the PC with the keyboard flap close.



I have glued aluminium foil onto the wood for shielding. The wood made the box heavy, especially since the wooden frame needed to be strong. That is the reason why I have decided to use a lightweight aluminium frame for the new PC, and 3mm thick hardboard for the sides. Furthermore the motherboard of the new PC is mounted on its own base plate, which will not flex, even if the frame flexes.

With the old PC I have not removed the monitor from its housing, I have build it as is into a box. The main purpose of the box is to make the monitor rectangular, which eases storage as well as transportation. The top of the box is not fully enclosed to allow for ventilation.
 
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