Irrigation Repair 101

Third in my series of home repair items ... the rain sensor for my irrigation system. The function of the sensor is to detect rain - and then inhibit the operation of the irrigation system for a period of time, so that the system is not on unnecessarily.

It had needed to be relocated from it's old position - and as part of reconnecting it, I though I'd test it as well.

Unfortunately, it didn't want to work in the new location. Rather than buy a new one, I thought I'd open it up and see what the problem could be.

They are quite simple devices ...

• a sensor, which consists of a number of fabric type discs stacked on a rod
• when the discs are exposed to water they expand
• which in turn presses a micro switch

I disassembled the unit - and tested the micro switch - which was all ok. This particular one has the three leads: 

• one common
• one for a normally open circuit
• one for a normally closed circuit

This picture shows the bottom of the pole protruding into the chamber which houses the micro switch.

The discs themselves also seemed fine. I gave everything a clean, and reassembled.

And here finally is the result - the irrigation controller showing the rain symbol.

I can only guess that the process of relocating the sensor disrupted it in someway. But, a working sensor makes for a happy gardener.

Door Chime Repair 101

Following on my theme of repair, rather than throw away and replace ... my attention turned to my door chime - which had not been working properly for a while.

It's a simple model - an Arlec DC371 - $35 retail. After changing batteries in the receiver and transmitter, it was still not cooperating. But, in looking around inside the transmitter, I inadvertently pushed the button to select the tunes - and it sprang in to life.

So, I knew we had some basic functionality. I returned to the circuit board, and inspected the main micro-switch for the pushbutton. It had two leads protruding from the other side of the circuit board - so I shorted the switch output with a screw driver, and hey presto - it worked.

The cuplrit was the micro-switch. And they don't call them micro for nothing.

It looked a little daunting. The top plastic retainer was fixed by 4 little plastic lugs. I sliced those off, and underneath was a small plastic button, sitting on top of a flexible metal disc - which was slightly convex, so that it clicked when depressed.

Under the disc were 3 contacts - two at the sides, and one in the middle. When the disc was pressed, it closed the circuit between these contacts. I removed the disc, and tried shorting the contacts with a screw driver but this didn't seem to work.

I gave the contacts and the disc a good scrape with a sharp knife, and a clean with some vinegar. And this seemed to be enough to allow the contacts to work. Result.

The tricky part was re-assembling the switch, since I'd cut off the tops of the lugs. I turned to my trusty super glue - but the first attempt failed - since it seemed to find it's way in to the mechanism.

I broke it down again, cleaned the parts, and tried again. This time was successful.

So, it's now back in operation. No more complaints from family and friends that the door bell isn't working.

I know I could have bought a new one ... but it's the principle, right?

Real World Usability

This is a post on usability - in the "real world" - which may become something of a series.

The subject today is a ticket vending machine - not super exciting, but it's a a new model being rolled out in south east Queensland, so could be considered topical.

First, a picture:



Mmmm, what ever could be a problem with this shiny new design.

Well. A few things unfortunately. Let's see.

1. the coin slot. There's not enough room for a right handed person to insert coins, without constantly scraping them up against the side of the machine. Why?
   
   
   
   
2. the "ticket/change/receipt" hopper is too low. I understand that the machine needs to cater for people of all heights, including wheelchair access - but this is just too low. It requires constant stooping to fetch change and tickets.
   
3. the touch screen. I'm not sure where to start with this one, since there are so many aspects ...
   
   1. the responsiveness (or lack of). there's a lag in the response - so that after you've pressed a soft button, you're not really sure if it's really pressed or not
   
   
   2. the angle - unless your eyes happen to be perpendicular to the screen, your screen presses will be off the mark - it seems that there is enough of a gap between the surface of the touch screen, and the actual LCD screen that this is a real problem.

Then there's the interaction flow. The series of screens you have to wade through to get a ticket is just plain cumbersome. Some issues are:

1. To select a destination station, you need to go through a multi level alphabetical menu, or select from a "map". The map isn't too bad, but in combination with the "angle" problem, it's a little hard to use as well.


2. There are no direct keys for common stations


3. why not allow a one touch "daily to Central" from suburban machines?

I realise that these concerns will not be as prevalent once the smartcard side of things is operational (since most commuters will just use them to top up the value on their cards) - but they will still be relevant for paper tickets.

A little bit of research shows that these machines aren't a one off design for Translink - they're a customized version of an existing design which goes by the name of "Universal Vendor 1000". I wonder how much usability testing they did?