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Revisions – already

Alright, so I couldn’t leave well enough alone. I was looking at my main board during lunch and realize that a little reorientation of the power supply would better position the fan and power headers, as well as putting the sensor headers closer to the back of the control box (meaning less medusa factor). It puts the 120V AC traces towards the back of the control box and the weaker 5V at the front – also a very good upgrade.

That ended up freeing up alot of room at the top of the PCB, so I proceeded to route this snakey looking transmitter antenna through that area (as a just-in-case). This will let me do on-the-fly testing if the signal strength is weak, and if the PCB spiral isn’t enough then there is a pad at the end to solder in an external antenna too… That extra real estate also means I’ll have clearance to get the fuse in and out a little easier. I’m hoping I’ll never have to replace the fuse… but again, “just in case”.

I also realized I had 3 jumper wires for the sensor signals to accomodate the ground trace, which with a little rerouting and a different jumper trace for the onboard LM34 temperature sensor, I reduced the number of jumper wires by 2. That’s 4 less drill holes and 4 less soldering points.

I do wish there were a good alternative to the ULN2803A Darlington Driver IC…. its got 8 channels, and I’m only using 2 of them to drive the SSRs. I don’t think they make a DIP8 package version, so I’m probably stuck with the wasted space and pins. I am considering snipping off the posts of the IC socket that won’t be used, meaning I’ll only drill 6 holes for that IC instead of 18… and the the IC will remain whole since it’s plugging into a socket. Still a big waste of space, though. I suppose I could use a couple of single Darlington pair transistors to drive the SSRs… But I like the IC approach better.

The fact that my drill press isn’t here yet has yielded positive consequences so far – it gives me more time to obsess and refine my design before settling on something and producing the circuit. Who knows what this will look like if it takes another 2-3 weeks…

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