We introduced this new Digital Lighting Sequencer last month and already it’s created quite a stir. So how many budding Chevy Chase wannabes are there out there, anyway?
This month we’ll go through the relatively simple construction of both master and slave units, testing them and then how to use them. We’ll start with the smaller of the two “boxes”, the Master Unit which has all the “smarts”.
Above is the master unit with a 128MB SD card in its reader. This is connected via a suitable length Cat5 cable . . .
Master board construction
Before assembly, check the copper side of the PC board for defects and that the holes are drilled correctly. Test the connectors for fit. If your board is not provided with the corners cut out to suit the case, you will need to file it to shape.
First install the SD/MMC card socket, which goes on the copper side. Remove the dummy plastic “memory” card, then place the socket over the pads. Check that they all line up, then apply some solder to the two larger mounting pads. Ensure it is aligned and that it is sitting flat on the board – if required, re-melt the solder joints and adjust its position.
Once it is in place, apply solder to the 13 remaining pads, ensuring that the solder flows properly onto both the pins and the pads. In the case of the Altronics socket, one of the mounting pads has two pins (one is ground) so make sure that the solder covers both.
Fig.4: here's the component overlay for the master unit, with a matching photo underneath. Two points to note: (a) the SD card socket is mounted on the underside of the PC board, and (b) the 2200μF capacitor is mounted lying down on the PC board, with some hot melt glue or silicone sealant to hold it in place (after soldering!). We strongly suggest you use a socket for the microcontroller at least – it makes testing and trouble-shooting a whole lot easier. Note that there are some minor differences between the early prototype PC board at left and the component overlay above.