So, in the last blog entry I told you about the perl DMX backend that we are doing for the party project of ours.

We have concluded that we will have a bitchin’ intro show. And it will be timecode controlled. Every little audio / DMX / Video effect will be timed to the millisecond.

To do this, we have (for now) concluded that we will use Ardour as the audio platform, and use jackd as the timecode server.

The nice part about this, is that it’s very easy to code a jack client that fetches the timecode in realtime, and then transmit it via UDP to our external timecode display. And thats where this blog post comes in place; we are creating a cool 8 digit 7-segment display to display our timecode.


William got 8 of these modules from Kay, who agian bought them for almost nothing at eBay. :D (in Norway they cost about $25 each at the time of writing)

Anyways. As you see in the picture, william has glued the 8 digits together, wich we will put inside a box, and wire up with some pic18f4520 and some ENC28J60 for ethernet connectivity. Yes, the module will be stand-alone, only connected to ethernet, and display the current timestamp/timecode in Ardour/our DMX system.

Do we _really_ need it? no. Is it really cool? yes.

So, so far we have finally gotten the box for the device. It’s acctually a image frame, with an exceptionally deep frame on the backside to contain the whole shebang.

Here are some more “under construction” photos:


In the first photo you can (almost) see the PIC18F4520 on a vero board, with a connected prototype board with the ENC28J60 chip, which works perfectly and successfully outputs data to the (soon to be connected) displays when it receives timecode UDP data on port 1337 ;P

This project has not been the easiest, even though the concept is simple. I’m not the greatest engineer in regards to analog electronics. The problem is that the 7segment displays needs 7.2v, and uses common anode. This means that I cannot use the displays directly from the PIC processor. So i went on using a ULN2803A to drive the display. This solves the “common anode” problem. Now on to solving the 7.2v problem. I have as I said, not very much to say in the analog electronics world. So I went on, and found the first PNP transistor I could find. Kay was kind enough to donate them to us.

He had a bunch of 2N3906 transistors, wich seemed to be “workable”. So i set them up on a breadboard and after some fidling with resistors and pulling up the signal, to let the PIC pull it down, to enable the flow trough collector and emitter. This seemed to work great, so I soldered the whole shebang together.

Everything works great now, except that the display “fluctuates”. Seems like either the 5v regulator is too weak (it gets pretty hot, but I can’t check it, because my multimeter doesn’t want to measure current), or the transistors are a bit too sensitive. Sometimes, when there is traffic on the network the display fluctuates when the ethernet-leds light up. So something is not at it’s fully potential yet. But I’ll measure a bit when I get a working multimeter.

So here are the latest images(only thing missing is the 4 dots at the bottom):

I love doing statistics of everything, because data is power. So we thought we would put a temperature sensor in every server-rack in this server housing facility, and I checked the prices of some standard components. First I thought of the DS1820, which is fine, but two drawbacks. It’s somewhat expensive, and takes a full second to read value from. So if you wire a lot of sensors serially, you’ll need to wait one second for each sensor on the same line.

Then I found these cute analog temperature sensors, called MCP9700A. And they cost only €0.37 each. Or if you buy larger quantites, you’ll get even lower prices. So I thought.. the PIC18F4520 has 13 analog ports. Why not create a small pcb with a pic18f4520, and some connectors, and wire it to the computer via RS232.

The problem then, is that i’d have to buy max232 chip, and then I’d need a RS232->USB cable, and thats pretty expensive. But then I found the life-saver chip FT232R. This awesomeness in a chip enclosure is a RS232(or any serial data in TTL levels)-to-USB ‘converter’. It has drivers for windows *, Mac, Linux. And you can even modify the eeprom inside it, to make it use a different VID and PID or just change the device description of it. And it also have two GP pins, which you can connect to LEDs to show when it sends or receives data. The BEST part about this already awesome chip, is it’s price. Here in Norway a RS232->USB cable costs from €42 an up. But this device, practically the same (except for missing RS232 level converter), costs only €2.87. And thats with all the leetnes of being able to change the device description and all, included.

So I wired it all up in Eagle, and it came out to be like this.
Schematics:

Board:


So here I have a PIC18F4520 processor, 20Mhz XTAL for it (because I had some laying around), FT232R chip, 100K Resistor pack, and a few LEDs. All in all, about €20 worth of components.

So, now that I had designed the board, how to get it made, and cheap? Well, I found this site called [link]www.batchpcb.com[/link]. Which is fabulous. They collect PCB boards for a bunch of people who need cheap prototype boards, and send everything together to China, where they produce the boards, and return them in about 12 days. They often set up your board several times, in case some of them should be bad. (bleedout on the copper). And the best part. If more than one of your boards are ok, they even send you the extras, with no extra charge. So I received two pcs of the PCB I ordered, and couldn’t be happier :)

Here’s the result, (image quality courtesy of iPhone 3G)


Then we add all the components. And bobs your uncle: (image quality courtesy of iPhone 3G)


And it even works! ;)

The software I have uploaded to the PIC18F4520 sends all the temperature info, and the 8 general purpose inputs to the computer via a virtual com port on the computer, 20 times a second.