Unknown Domain

Do I detect a Split-flap Display?

On my way home today I noticed a hidden gem of Brighton Station, a old, very dusty old split-flap display nestled behind a newer information displays, along side it an electromagnetic flip segment clock. I am very excited that these are here, I know Southern aren’t likely to go running up there to take them down for me but I think it is worth a few calls, perhaps who knows there might be the rest of the units hiding in a cupboard somewhere. It can’t hurt to ask right?

*crosses fingers*

AAN: Arduino Area Network

Earlier this year I started to investigate how I might go about implementing the circuitry and communications between a computer and a micro controller for my long term split-flap display project which seems to have taken over my blog of late!

The setup I finally settled on was to use a simplex (single direction) serial protocol called RS-485, the ‘bigger brother’ of RS-232 used in almost every computer, commonly known as ‘the serial port‘. Using RS-485 would require some special circuitry which could convert to a signal that an Arduino could understand so I went about building a converter circuit which I had built up as a small PCB, my first proper PCB, designed by me alone, and it worked first time!

Next I worked on some software which is designed to receive six byte commands from a master control board allowing full control of all modules together or each module individually. The commands are structured as follows:

  • STX (Start of text)
    Denotes the beginning of a transmission, the ASCII byte 0x02.
  • Address
    A byte representing the intended receivers address. 0x00 addresses all units and 0x01–0xFF are receiver addresses, 255 unique addresses in total.
  • Command
    A byte representing the command:
    0x00 – Blank all units (Go to space character).
    0x01 – Control status LED on main board (0x00 = off, 0x01 = on).
    0x02 – Reset (Clear EEPROM lockout).
    0x03 – Store new address in EEPROM.
    0x04 – Go to flap.
  • Variable
    Depends on command byte.
  • Checksum
    This byte is the value of all other bytes XORed together, to help ensure the integrity of the received data… STX ^ Address ^ Command ^ Variable ^ ETX = Checksum
  • ETX (End of text)
    Denotes the end of a transmission, the ASCII byte 0x03
This command protocol is simple but effective for my needs, it has plenty of space for expansion of the command set and the one byte address range is plenty for a single ‘universe’ (DMX speak) of modules as the RS-485 chip I use has a theoretical maximum of 256 devices on one chain, and including the command module and 255 addresses that is reached using this protocol.
With the RS-485 board finally working I started looking at building my own basic Arduino, based off the open source schematics and Standalone Arduino I meticulously designed a schematic in EAGLE for my own Basic Arduino, and then laid out a PCB and set it for fabrication with OSH Park. This board came back last week and I assembled all three, to my amazement they all worked perfectly first time also!

The next thing to do was hook up both my boards as originally intended and use my command protocol to test the devices, even on just 9600 baud I am able to make the LEDs dance one after the other like a fair ground attraction using the computer as a controller.

You can see in this video the end result which I am very pleased with, to have all three work perfectly and do what I originally intended is absolutely amazing, and really gives me the confidence I need to push on and work on the sensing of flaps passing and homing of the deck then trying to combine the two schematics I have designed with the EasyDriver and a few tweaks to produce an all in one module controller board which hopefully will work as well as the previous two boards. I may look into using SMD parts too!

If you want the schematics I have posted them on GitHub:

Basic Arduino
RS-485 Adapter

Found images…

Today I tried out an application called Lost Photos which is free today only, it retrieves images from your email account that you may have lost.

I thought I would have a go at it and it found 2,500 photos! Rummaging through them many I have already posted up here, however I found the first set of images I was ever sent of a real unit, from a member of staff at Network Rail, Tom Chaffin, for some reason I wrote about my email to him, however never posted the images…

Split-flap design…

Another day, another split-flap display project, the streets of Ginza, Tokyo, Japan now feature an interesting animated window display by design agency Drawing and Manual for client ISSEY MIYAKE INC. a clothing retailer.

Source: CreativeApplications

Omega

Until today I had only discovered two manufacturers of the split-flap displays of days passed, Solari and Krone. Today I have another, Omega, the departure boards and track signage for Grand Central station has recently been overhalled by a restoration firm called Olek Lejbzon & Co. this firm replaced the old split-flap displays with new LCD units while refurbishing the existing (listed) housings.

The firm have been gracious enough to send me a bunch of photos of these split-flaps and I am in the process of negotiating the purchase of one or two of the units. They are very old by the looks, the design is much more rudimentary than the Krone split-flap displays featured in my post about Jave.de’s project.

For more info about Olek Lejbzon & Co.’s restoration of aspects of Grand Central Station, take a look at these two pages:Hutchinson Track Indicator Restoration, Other. Thanks again for the images…

Circuitry

So for the past couple week’s I have been working on building up the circuitry, previously I designed, ordered and built up the RS485 board as shown on the right.

The board worked first time thanks to my careful testing and after some debugging of my own stupid mistake which I made not once but twice it worked like a charm.

To test it I hooked up three Arduino’s in a daisy chain with the three identical RS485 boards in Receive mode, and hooked up a USB to RS485 adaptor I bought on eBay, the code was simple, if it gets a 0x00 byte it turns off a LED, if it gets 0x01 it turns on the LED, and surprisingly it worked!

You can see in this diagram how the process worked, and the above image shows the CAT5 cable passthrough connection which means the devices daisy chain easily.

The interesting part of RS-485 is that it uses differential signalling, put basically as you can see on the right the two signals are opposites of each other, which means that the signal is more resilient to noise as the idea is that the two cables are twisted pair (like CAT5) and so they both experience the same noise but are polar opposite signals so the binary output can be determined by looking at the difference between both, this eradicates noise issues.

The board I have been working on this week and a bit of last is the standalone Arduino circuitry. As I am not a micro controller or electronics guru, I want to stick with what I know which is Arduino, however these boards are quite expensive and offer more than I need. My intention is to build a basic Arduino into the circuitry of my project. To do this I needed to do a lot of research and understand what parts are essential.

I have designed and tested on a breadboard the schematic for a basic Arduino and today sent it to be manufactured like the last, I hope it works as well as the last PCB I made so I don’t have to wait another two weeks to get it back, however the idea of making multiple smaller boards that are modular is I will combine them together in one design at the end to make one unit which means it should just work rather than having to mix multiple parts together that might make it harder to debug.

Plastics

Today I got two sample packs, one from VitasheetGroup which had the wrong stuff in, it was two sheets of the stuff I bought from Pullengers Epsom, and two sheets of white 0.5mm PP with the G01 finish, it’s great because I have something to check the finish is right against, however it’s no good from the perspective of thickness, additionally I can’t really order it because no one sells small quantities anyway.

The other sample was from Saffron Plastics but turned out to be a plain finish i.e. no finish, which was no good and it was 1mm which just seems a bit too thick.

Stephen Webster didn’t answer my email so I called them and a nice chap gave me some quotes for what I want which is ViPrint G01 Black 0.8mm, MOQ was 1775 sheets at 880x440mm, the price per sheet was 84p which is adds up to £1,491 + VAT & Shipping, this would be about a 500 KG of material!

On the plus side he did say they have 950 sheets of ViPrint White G01 0.8mm in stock at 1100x650mm for £1 per sheet which means I can get the right material in the wrong colour and go with that. He also sent a price guide for their stocked material which is all in the infamously crap G02 finish, page from the price list is here: Price List.

I’ve emailed them to see if there is a possibility of piggy backing on another customer who does make large enough order, and about getting 5 sheets of the white as it’s a good price even if it is the wrong colour.

Reorganising

Now that I am not at the Royal College of Art anymore, at least until the new academic year, and with a light schedule of work until graduation next year. I am getting geared up a bit better, my house mate and his girlfriend encouraged me to bring my main computer into the living room where he has his desk, we’ve created a floatilla of jubilee proportions in desk formation.

Luke’s desk, behind mine is a long piece of discovered kitchen work surface stretched across two builders benches. My desk as shown below docks into his desk but has a bit of a raised edge that leans on his. At the left of frame is the kitchen table and that completes the flotilla. This enables me to work in an office situation away from my bedroom which is all the rage in the so-called ‘real world’ and apparently better for sleeping patterns.

With the space left over I have reinstalled my original (came with the house) desk which is basically two battens across the wall, another spare piece of kitchen work surface and a corner support post. This is strangely too high to sit at but too low to stand at, must be an Olympic standard kitchen surface? Anyway I have reinstated it to make a space for my electronic’s and projects area. I will need to get a piece of wood to protect the surface when soldering but otherwise I think it will be a good solution for the foreseeable future.

Note the letter ‘T’ peeking over, this is the V2 prototype that I have yet to photograph, sitting on top of the larger V3 prototype (hidden by my fancy new, second-hand Phillips analog scope).

Plastics (again)

I called Vitasheet Group again and spoke to one of the staff there, she has gotten me an email address for the UK distribution manager and someone who can provide samples for checking which finish of 0.8mm black polypropylene I would like, the UK distribution manager is the previously mentioned Jed Brooks (jed.brooks@vitasheetgroup.co.uk) and the sample person is Stephanie Penin (stephanie.penin@vitasheetgroup.fr).

The person I spoke to on the phone suggested a few possible suppliers although she admitted she wasn’t involved with the PP side of things any more, all are new to my search so I will be investigating.

I will be getting in touch with these companies to see what they offer, hopefully I can get some of the G01 (smooth/smooth) finish rather than the G02 (smooth/textured) finish I have been able to find thus far.

Die cutting

One of the issues I have been facing is that the laser cut flaps cut quite well but the black finish is damaged by the high temprature gases that are formed under the cut material.

When the laser point hits the polypropylene it rapidly heats and vaporises the plastic, creating hot gas which pools under the material in the honey comb grill. This leaves a white smokey debris that can be cleaned off but also leaves heat damage.

For many materials this isn’t really a problem because the melting temperature is higher and many materials come with protective plastic stops scratching but also offers protection against this gas. Polypropylene however doesn’t come with this protection as 0.8mm thicknesses, additionally polypropylene has a particularly low melting temperature of only 150ºC which means at anything over 100ºC it can easily begin to effect the finish of the plastic.

The solution to this is to use die cutting, which would have been the method of choice for Solari, Kone and other manufacturers as it allows hundreds of flaps to be produced per minute and the cost of tooling a cutting die reduced the more you use it, while the laser cutter costs remain constant.

With this in mind I asked around some graphic designer friends who they used for die cutting and one came back and suggested Medway Cutters I asked them for a quote for a die cutter for personal use with my design as well as some small runs having them do the work, prices include VAT, exclude postage:

  • 1 up cutter = £90
  • 100 flaps = £96 (96p per flap)
  • 500 flaps = £222 (44p per flap)
I have asked them for a sample of the quality and how many flaps they expect the 1 up cutter would last, looking at these costs it is pretty expensive and doesn’t seem to run with what the cost’s I would have expected, additionally it doesn’t match the laser cutting costs:
Cutting time: 10p per flap (5 minutes x 75p = £3.75 for 36 flaps per sheet)
Material: 5p per flap (£1.63 per sheet ÷ 36 flaps)
Total: 15p per flap (£7.50 per module)

The flap design is probably going to remain the same now so here is the pattern: