Of the many concerns involved with a custom installation process, here are some of the notable things you need to consider.
When browsing this page, you may find it useful to view pictures of my own finished installs. I have a gallery for this in the Custom work section of the site.
· Board size: Believe it or not I have found this not to matter so much. One tiny board seems to work just as good as another tiny board. The only time this should make any difference would be if you wanted to use one of the alternative retrofit boards in your custom install, being that the alternative board is "small enough" to work. But when speaking for multi-purpose boards, it'll be uncommon to find a situation where one tiny board is just not tiny enough compared to another.
· Board indicators; use of LEDs: When planning the install it's likely you'll want to consider how the board status will be monitored. This means how you will use the board's indicator LED or LEDs to see its current status, or use a display screen if available. Most boards have an LED mounted directly to them and if that's the case then you'd have to mount the board so the LED is visible from the outside. The alternative is to remove the LED from the board and mount it someplace externally-visible, then attach the mounted LED to the controller using wires.
In the first picture above, you can see the yellow/black wire pair which leads to the relocated LED at the rear of the marker. This was easy to do since the Morlock original uses a through-hole LED, but may be difficult for a board with a surface-mount LED (such as a Mini-Morlock). The second picture shows two cases where I had to relocate the surface-mount LED on a Mini-Morlock board. The wiring for surface-mount relocations is fragile and has to be tended carefully so the solder pads don't get ripped up.
Boards specifically-designed for relocated LEDs will be both good and bad. The good part is that if you planned to relocate the LED in the first place, you won't have to do any additional work for it. The disadvantage to this type of board is, however, that you're forced to mount the LED someplace else. This adds to the wiring of the board and can reduce the reliability of the install.
· Board control; use of powerswitches: This factor determines how the board is activated and deactivated. There are two possible options:
1. The board uses a momentary button which tells the microcontroller to turn on or off.
2. The board uses a two-position switch which is spliced into the battery wire. This physically cuts the power to the board; the board itself is always on so long as the battery power reaches it.
There are advantages and disadvantages to both types. The advantage to a momentary switch is that they're typically easier to operate, however their disadvantage is that they leave the battery plugged in continuously so the battery will be slowly drained by the board's capacitors while idle (this will be slow if the capacitors are small, but may be much higher if the marker uses a larger solenoid with a large capacitor). Two-position switches are oftentimes easier to install and also a bit more reliable, and you can leave the battery plugged in indefinitely, but their disadvantage is they aren't always an instant-off if the marker uses one of those large capacitors.
At the moment, there is no such thing as selection between these two options; every board out there forces you to use one method or the other.
The first picture above shows an installation involving the battery wire spliced through a slide switch. As mentioned this is often much easier to install, and will also be better in terms of wiring (since there will already be battery wires, no additional wiring will be needed for the switch). However this only works well with a marker not using an additional solenoid capacitor.
· Eye support: Most boards out there will support beam-break eyes since they're typically more reliable. However, when performing a custom-install you may find it much easier to use a reflective eye since it only requires one hole to be drilled in the marker breech. Beam-break eyes require two collinear holes be drilled to face each other and that can be much more difficult to perform.
Thus, a board offering support for both beam-break and reflective eyes is ideal since it gives you the choice in which eye system to utilize. In most cases it will be easiest to simply follow the stock hardware, however even then you may need to modify the existing parts, or install new ones in place of the old. In other cases you can completely ignore the stock hardware and install the opposite, if it suits you. I've installed reflective eyes in Ions before, for this very reason.
· Input voltage maximum: This comes into play when working with E-Mags. Most markers use a standard 9v battery (or they can use a standard 9v battery) with the exception of the E-mag and X-Mag which used a huge 18v battery/solenoid. In order to operate the E-Mag solenoid you need to supply it with 18v, so a board capable of taking only 9v will fry if fed with the Mag battery. The vast majority of boards out there will not work with the 18v Mag battery (assume your board won't work unless told otherwise). Both Morlock and Proclus boards will work okay with a Mag install.
· Solenoid drive: The circuit board's hardware can determine whether or not it will work with a specific solenoid power requirement. Markers using large-coil solenoids require high-power transistors to operate correctly. Examples of these solenoids would be those found in sear-tripper markers, MAC solenoids, the Ion solenoid, Mini solenoid, and some Humphrey solenoids. If the board doesn't have enough power to drive the abnormally-large coil, it won't be able to actuate the solenoid. Chaos 2k7 boards, for instance, can't run heavy solenoids.
Sometimes the circuit can be modified but this requires electronics and soldering knowledge.
· Solenoid signal: Some solenoids (large-coil solenoids as listed above) require special solenoid pulses to function correctly. The solenoid signal for most markers is a straight on for the dwell time; pulsed solenoid signals are on for a short amount of time then the rest of the dwell is pulsed up and down very rapidly (many times each millisecond). This helps to lengthen the life of the solenoid by reducing heat buildup, and also conserves battery power. Not all boards are programmed with solenoid pulse support, so if you pair up a board with no pulse support with a large-coil solenoid, the life will be shorter and the battery will drain quicker. Alternately, if you use a pulsed signal board with a solenoid designed for a straight-on signal, the solenoid may not fire correctly. For instance, an Ion board (which pulses its solenoid signal) is unlikely to function well with most Parker solenoids, or other indirect-acting solenoids, although I can't say for certain since I've never tried for performance value.
· Connector design: This is a huge factor to take into consideration. Ideally you will want one connector for the body components and another for the frame components. This allows you to separate the frame from body without adding additional connectors. If the connectors are the same, however, the marker body becomes tied to the frame via the wiring. The old PredatorII boards used many small connectors however it took them a step further and actually used too many connectors. The installation with Predator2 boards was an absolute ratsnest of wires (picture) leading to the board's eventual discontinuation.
Unfortunately most multi-purpose boards only offer one connector, so you need to add additional connectors. You can try your hand at using locally-available connectors where needed. Radio Shack sometimes carries things that are useful, however it's likely that the connectors they offer are too large or require too much force to separate. Whenever I had to install secondary connectors in my own installs, I used Molex Milli-grid connectors which are the same as Bushmaster/Morlock/NME boards (picture; picture). I actually sell these parts if you need them, although I'm not trying to plug myself (I use these connectors in virtually every wiring problem I have, paintball or otherwise).
· Solenoid configuration: Most markers out there use only one solenoid to operate, however if you're using a dual-solenoid marker then you will require extra support for that. This includes a Shocker Sport (or pVI Shocker), Excalibur, Sovereign, Autococker, Nova, Epic, Mayhem, and some others. The markers using two solenoids will require both of them to operate independently from one-another. The closed bolt markers using one solenoid (Nova, Epic, Mayhem) will have to use the same boards from a dual-solenoid marker, since the logic is the same.