Wedding? Present!

It is Wedding time again

No no, not for me. A friend is getting married: the sister of my Mums godson (is there an english word for that? There is none in german :-)
Sister-of-godson is basically family.

This calls for a present

And so it is time to make a wedding present.
Make, not buy – bying is only half as much fun.

Building extensive "wrappings" for presents is a habit I picked up from a friend. But more recently I modified it: make something, that serves as a packaging for a present and is a - more or less - useful object by itself. Note to self: add links to other pages here for more examples.

For the impatient: When I tested the opening and closing using the internal mechanism, I did record that with my old Nikon Coopix. Its not cinema-quality movie, but You'll get an idea of what the box does.

Project start

As in every project, there is the first step: the kick-off. Here I decided to actually attend the wedding construct a present rather than buy one * make the contruction a true „hase“

Ideas

Next step: analyse the prerequisites and environment.

• The present had to fit into the line of wedding presents I have made over the years.
• It had to be something you would not expect form anybody and that you would immediately associate with me when you saw it.
• The present had to be fun.
• This time, the construction should be more than just a self-opening packaging, it should be the actual present. And it must serve as a packaging for the presents that my Mum and my brother made for the bride.
• It had to use electronics (which is part of "true "hase").

Using something electronic in a wedding contraption is actually a new idea (for me). So far I made a point of not using electronics but just electromechnical stuff (switches, relais and motors) in the presents.

This time I wanted to use electronics, probably a microcontroller.

One of my favourite online-shops Pollin had a special recently. BTW: I love Pollin because so much stuff they sell is actually quite crappy. So it is all the more fun to make something with it.

They offered what is known in Germany as a „Nummernschalter“ (if you do understand the buerocratic lingo of Deutsche Bundespost Telecom, that is). The non-initiated German would probably call it a „Wählscheibe“. Yes, indeed it is an old-fashioned rotary dial from a telephone. The ones offered by Pollin were used units but working fine.

Decoding the output from these is a few lines of code for a microcontroller, so this makes a very nice input device. I had two of these sitting around for a while and no project to use them on – so this project needed to use one. When using an input device like a rotary dial it is probably a good idea to use some kind of display as well.

I thought about not using a display since good old telephones did not have one either. Two reasons made me use an LCD anyway

• it looks so much more high tech
• it provided me with a way of debugging the fuction of all components while developing the firmware.

I had already used LC Displays before, so it should be a no-brainer to use one on this. I even had a small type lying around. The 2 lines of 16 chars each it shows were a little small in other projects, here it would be perfect.

Other ideas.

I just love modding existing stuff. Preferably stuff people will immediately recognize. This is usually true for anything Ikea.

Whether you hate Ikea or love it, whether every room in your house/flat/cardboard box hase some Ikea stuff in it or none – you certainly know Ikea.

The two-drawer mini-chest-of-drawers named Mackis (removed from the Ikea catalogue since my original posting, so no link here) is one of the well known products many people immediately recognize as Ike or as Ikea-style. So it should be a wonderful base for modding. I simply bought one and then started thinking about what to do with it. The original idea was to put a motor inside so it would open one drawer (or both) and close it again.

To cut a long story short, I could not figure out a simple but efficient and reliable way of opening and closing a drawer without rendering the other one useless. Actually I had a couple of ideas but none seemed to fit in the remaining time budget. Unidirectional motion is more simple to create.

So I went for the obvious solution: move one way only and use gravity for the other direction.

I found these sprockets and the chain in the catalogue from Conrad

The chain looks just like a bicycle chain, just much smaller. It is about 6mm wide and the links are also 6mm long. The sprockets match this, so they can be used to pull the chain or make chain transmissions.

The plywood in between the two drawers of the Mackis thingy is 5,6mm thick. In theory a 6mm wide chain would not fit in there, but actually it does because of the tolarances of the drawers.

Ideas summary

So we have some components and an outline of the overall idea

• Ikea Mackis becomes the base for the construction.
• A chain mechanism will pull the drawer out of the corpus
• A rotary dial will be used for input
• a small 16x2 LCD will serve for human interaction

That is a good start. Looks promising.
So lets make the thing.