Kaliko Systems Limited

Mounting, Wiring & Labelling

I want a "clam shell" type layout within the case to make it easy to assemble. To achieve this, I mounted the relay board on the inside of the case's lid and used flexible wiring from the board to the plug and sockets in the case bottom, as seen below.

Mounting

As all my relay boards have status LEDs above the board, then I need to mount the relay board upside down on the lid, so that the status LEDs can be seen through holes in the lid. To avoid bolts through the case, I want to mount the board using self-adhesive PCB pillars. However, as the relays on the boards are quite high this requires the pillars to hold the board about 16mm from the lid. These tall PCB pillars are a little more difficult to find than shorter ones, so you may need to search for them on the Web. The pillar's feet need trimming and rotating to clearly see the status LEDs. Simply viewing the LEDs through the holes in the lid restricts their viewing angle, so I have used LED light pipes to give a good viewing angle. Alternatively, as often the LEDs will only be viewed when installing or diagnosing problems, then you may not find the restricted angle a problem. Without the light pipes, the circuit board needs to be protected from anything coming through the LED viewing holes. A piece of thin clear plastic sheet can be cut to fit between the PCB pillars' feet and will then be sandwiched between the relay tops and the case lid. For the relay board that I used, I had to removed the front sections of two of the pillar feet, so that the computer connection socket on the relay board is hard up against the case side. I also had to take a nick out of one of the feet and rotate two of the other feet to place the light pipes. Then I made a rectangular hole in the case side for the plug on the cable from the computer. This hole's size needs to match the plug type on your computer cable. With many plugs, the thickness of the ABS stops the plug from fully engaging into the boards socket unless the ABS hole matches the plug's outside size. This is necessary, as a loose plug connection will probably fail in the future. A relay board lid mounting, illustrating the cut pillar feet, rotated feet and a light pipe (clear plastic rod) is shown below.

Wiring

The wiring is logically 3 parts:

1. Neutral and earth from the plug to the sockets. This wiring is all in the case bottom and is neatest in solid core tinned wire. Daisy chain through the connector pin's holes and add insulation sleeving where any wires cross, as shown in photo below. I recommend using a heavy-duty electrical soldering iron as otherwise it can take a long time.
   
2. Live from the plug to all 8 "common" terminal connections on the relay board. This is best as a combination of flexible brown wire from the plug to a solid core tinned wire bus around the relay board. The bus needs to connect all the "common" terminal connections on the relay board, so the shape of this bus depends on your relay board. The bus can be given some insulation by wrapping it with a partially slit piece of brown sleeving, then using brown insulating tape around the slit. The bus for the relay card I have used can be seen extending round the board in the top photo, and is shown in detail below.
   This split sleeving does not provide protection from mains voltages, as it does not cover the terminals or the board tracks that may be live. The case should never be opened with a mains cable or any controlled equipment connected (only the computer data connection is safe).
3. Switched lives from each "normally open" terminal connection on the relay board to each socket. This needs to be made from flexible wiring and formed into a loom. One relay board I use has two sets of 4 relays, so here it was best to create two separate looms. The loom(s) should to go via a side or end of the case to allow the lid and relay board to be easily unfolded ("clam shell" layout). Small cables ties can be used to hold the loom(s) together.
   

If the case is dropped from a height, as the relay board is heavy, then one or more of the PCB pillars can become detached. So I added an insulated separator made from 3mm thick MDF board. This good fitting separator between the relayboard and the connectors in the bottom of the case will protect the circuit board (and computer) from this and many other potential accidents. This separator has corner cutouts to allow for both the ABS case's pillars and the wiring loom(s) as can be seen on the right in the top photo.

Labelling

Good labelling is very important to the final appearance of the case and its usability. The ideal labelling method would be silk-screen printing, but it is high cost in small volumes. A low cost alternative is to use a panel labelling kit, these use either photo-sensitive chemicals that requiring exposure to ultra-violate, or a  laser printer where its heat and toner reacts with special colored vinyl sheets. I chose the laser printer method and white sheets, as mono laser printers are now low cost and I wanted white text on a black background. Unfortunately the relay board's status LEDs are typically not bright enough to shine through the white vinyl, so holes are needed in the lid's label. After printing a suitable size hole can be made through the vinyl label by using a single hole paper punch (a drill just makes a mess). Shown below is the labelled lid (note, the label edge does not show strongly under normal lighting conditions).

Assembly and Test

I will assume that you have already separately tested your relay board. Such that using the board vendor's software, with only the computer's data cable connected and, if required a low voltage power connection, this results in you hearing the relays on your relay board clicking. Additionally, I suggest that you use a multi-meter or continuity checker to check that the "NO" and "NC" labels on one of the relays are the way around that you expect, as both users and manufacturers can get this wrong (for both "NO" and "NC" the N is for normally, as in the relay is not energised).

Now try and put the case components together to check that it all fits. The separator board should be a tight fit between the case bottom wiring and the tops of the PCB pillars. If too tight, then check if any case wiring bends upwards. Once you are happy that it all fits together, then check all the relay boards terminals screws are tight and give each brown wire a small tug at both ends to see if any come loose. Finally, one last visual check before screwing the case screws down.  Now use a multi-meter or continuity checker to check for continuity between all the earth connector pins, same for neutral pins, then for live pins, and finally check for no continuity between live, neutral and earth. Remember for live pins continuity, when using a fused case plug, you must have inserted that fuse. Low-power electronics equipment can give rise to high current surges, as their capacitors charge, so always use slow-blow (a.k.a anti-surge) fuses with such equipment.

I suggest that for minimum live testing you plug a mains lamp into your relay case and use a neon electrical screwdriver to test that live and neutral on each socket is connected the correct way around.

That's the end of how to construct and test, so here is a list of the parts and vendors that I used.