108Relays -- Putting the K145 in a case

A Case for the K145

This article is intended as inspiration, for those who are thinking about wrapping their K145 board in a case of some sort. You won’t find a detailed how-to, but more of a words-and-pictures description of one man’s experience. (**see also the second article, for an alternate method)

Foundation
The starting point was to choose a plug-and-socket method for connecting the temperature sensors. I used RadioShack audio cable for the sensors, picked up at a surplus sale, and 2.5 mm stereo plugs and jacks, from a local electronics parts place.

The existing DB9 connector on the board doesn’t work too well for going through a case wall. So I picked up a chassis-mount connector, again from a local electronics parts place.

Having the jacks and the DB9 connector, I had a better idea of the kind of sizing needed for the case. The case I used was a Hammond polystyrene flanged unit – 112 x 62 x 27 mm in size. The flanges make for easy case mounting. The drawback was this case had card slots built in, so the case walls were extra thick. This meant having to revise the mounting technique for the jacks.

Note the LED in the picture. I saw a similar circuit (the QKits VK011) that makes use of a LED, and decided to incorporate an indicator in this project too.

Case Changes
The stereo jacks are made for mounting through a thin chassis wall. My original idea was to drill mounting holes slightly undersize, and force-thread the jacks into the holes. Due to space restrictions, I couldn’t get all 4 threaded in – 3 yes, but there just wasn’t enough room for manipulating the fourth. I ended up cutting out a large rectangular area in the case wall and gluing a piece of heavy brass plate over the opening. This I drilled for the jacks, and they were easily installed, using the supplied nuts.

Board Modifications
- Remove the existing DB9 connector, solder in a set of header pins in its place
      Doing this also provides a couple of mounting holes for the board.
- Remove the existing header pins for the temperature sensors, and solder in a different
      set of header pins
- Solder in header pins at the “F” and “C” selection locations
      The LED will be connected to these pins (with appropriate dropping resistor)
- Solder a jumper in place so that Deg C is permanently selected.

Putting It All Together
As shown earlier, I pre-wired the jacks, LED and DB9 with pigtail leads. Once these and the board are mounted into the case, it’s a simple matter to connect the pigtails to the header pins on the board. I used a RadioShack wire wrapping hand tool for this. The wire wrapping greatly simplifies the hookup process.

It’s difficult to see in this shot, but the LED is beside the DB9 connector.

The case is physically larger than needed to fit everything. But when hand-wiring something like this, having that extra space is a lifesaver. I also have ideas for hooking up a Max232 chip to provide true RS232 capabilities. That space gives me room for expansion.

The Sensors
As mentioned earlier, I used RadioShack audio/microphone cable for the temperature sensors. This is 24 ga., 2-conductor shielded. The cable is lightweight enough for easy handling, and the insulation jacket provides good physical protection. (**see the cable article, for more info)

The sensor shell is just a casing from a cheap plastic pen. It’s not waterproof, but does give mechanical protection.

All Hooked Up

NOTES

Adding a LED
The LED indicates when the board is connected and powered. Some serial ports may not supply enough current, and the LED could load down the circuit. I used a fairly big dropping resistor (2K7) to reduce the current draw to a bare minimum. The LED still lights up, just not as bright as it could be. As noted earlier, I wired the LED to the “F”-“C” selection points on the board. These were convenient points to pick power off the board.

An earlier picture shows a yellow LED waiting to be installed. I actually ended up using a blue LED. The blues tend to be high brightness, even at low forward currents, which helps with indicator visibility.

Parts Sources

RP Electronics (www.rpelectronics.com)
- Hammond polystyrene flanged case (Hammond # 1591BSFLBK)
- 2.5 mm stereo jacks (RPE # 352-804-1)
- 2.5 mm stereo plugs (RPE # 352-215-1)
- DB9 female solder connector (RPE # DBF-09)

RadioShack (www.radioshack.com)
- 2-conductor, shielded cable (# 278-513 on the website, # 278-1275 on my rolls)

Futurlec (www.futurlec.com)
- header pins (see this page: www.futurlec.com/ConnHead.shtml)

Qkits (www.qkits.com)
- K145 temperature data logger kit
QKits also has a range of cases/enclosures available.

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