​ ​ ​ ​ Little Ben - An outdoor chiming PICAXE clock
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Thread: Little Ben - An outdoor chiming PICAXE clock

  1. #1
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    Default Little Ben - An outdoor chiming PICAXE clock

    Little Ben is the brainchild of fellow sculptural artist and business partner, Philip Gamblen. Its structure is styled on the tower of Big Ben although on a slightly(!) smaller scale.

    Originally built for the public art exhibition "Sculpture at Bathers 2017" at Bather's Beach, Fremantle, Western Australia, the sculpture has now been purchased by the nearby City of Joondalup and was installed at the Penistone Park recreation facility, Greenwood, WA.

    Standing about 5 metres tall, Little Ben is made of powder-coated steel. The middle section of the structure houses 3 galvanised iron rubbish bins and 2 metal buckets to provide the sounds of the Westminster Chimes or "Westminster Quarters" every quarter hour and Little Ben to strike the hour count. Each bin or bucket has a solenoid driven striker mechanism designed by Phil. Their principle of operation is similar to the inertia action of the hammers in a piano, allowing the bin or bucket to "ring" more after being struck.

    Phil engaged me to link a real-time-clock to the solenoids, to give as realistic as possible rendition of the Westminster Chimes. The 2017 exhibition was for just over 2 weeks, so a DS1307 Real Time Clock (RTC) was interfaced with a PICAXE 28X2 mounted on an AXE401 shield board. A Sparkfun MOSFET shield was stacked on top to drive the bell's solenoids. The original installation, being temporary and adjacent to a beach, called for the clock to be powered from a 10W solar panel and a small lead-acid battery. Now permanently installed, it is powered from the 230v mains supply provided by the city council.

    Installing a microcontroller-driven "clock" permanently in a public park and having it keep reasonable time was a challenge. Using an RTC to keep time for the short term is OK but this clock installation needed to be low maintenance. (I.e. really low maintenance.) I had done some reading on GPS receivers which can output UTC time as well as the more commonly known geographic coordinates. A GPS receiver was sourced and found to operate from a 3.3v supply with a default data output speed of 9600 baud. The GPS receiver board needed to be housed in an enclosure that was transparent to satellite-sourced radio signals, so metal boxes were not suitable. Importantly, the IP65+ enclosure had to be mounted in the Little Ben tower structure in full Australian sun with summer shade temperatures exceeding 40 degrees Celsius, surface temperatures over 60 degrees C and be rated to resist UV damage. I managed to find a suitable enclosure, sourced from Europe.

    The Westminster Chimes are surprisingly challenging to replicate on a microcontroller. It must have been an interesting exercise to develop the mechanical version hundreds of years ago! The quarter-hour chimes start before the quarter-hour and finish just before the actual quarter hour, so must be started at varying periods before the respective quarter-hour depending on the time be sounded (:15, :30, :45 or :00). The hourly chimes-count starts on the hour. The software limits the chimes to daytime as prescribed by the city council.

    I used the 28X2's background serial reception feature as well as the PICAXE's software clock, with a timer interrupt. While very accurate, the GPS serial data is not 100% reliable although data glitches are quite rare. GPS data packets incorporate a CRC, represented as two ASCII-Hex bytes. I developed a CRC checking routine to validate each 'time' packet. Separate to the GPS-sourced time, the PICAXE's background timer causes a 1-second interrupt to maintain the hour, minute and second 'master' variables. The chimes are effectively driven from these master variables. Whenever a valid GPS data packet is received, the master variables are overwritten.

    I'll post the background GPS serial data reception software at a later stage.

    Little Ben 1-LR.jpg

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    I have been imagining this massive structure, and then the photo reveals a very minimal package! Where did you find invisible space for the electronics?

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    Quote Originally Posted by Texasclodhopper View Post
    I have been imagining this massive structure, and then the photo reveals a very minimal package! Where did you find invisible space for the electronics?
    As a visual artist, I must have a painted a larger-than-life picture in words! As I mentioned above, Little Ben is a little over 5 metres (18 feet) high. The budget was modest, so transport costs had to be considered.

    The electronics fit into an 150x110x73mm (6 x 4.5" x 3") enclosure, large enough to fit 3 stacked "shield" boards, plus a dc-dc power (buck converter) board and the GPS receiver and not much else. The steel frame is 75mm (3" x 3") angle iron, almost enough to hide the controller box. If you look closely at the top right cross-member, you can just see the top edge of the electronics enclosure (about 1 pixel high in the attachment).

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    Great looking. Can we get audio?

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    The attached audio track was recorded in our studio, prior to installation.

    You will need to download the file (Right click/Save target as...) and remove ".pdf", so that your computer can recognise it as an mp3.

    Lilttle Ben in Studio.mp3.pdf

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    Cool, thanks. I guess brass bells would have been outside the budget (not to mention that they would have been liable to have been boosted).

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    Penistone Park sits in the middle of a residential area, so bronze bells might have been controversially loud. Of course, being artists, we know that a bit of controversy can be good free publicity!

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