Tuesday, February 8, 2011

Mounting the MCU, electronics and probes

I've been a bit slack on the blogging.

Recent progress includes:

1) A housing for the RX62N including acrylic splash guard and push buttons.

The idea is to have the LCD at an angle where it is visible and to avoid the board getting wet should there be any splashes.

The cover is hinged so that I can get easy access to the board for programming.

2) Electronics re-work.

As seen in the other posts I had the electronics board mounting directly on top of the RDK board via some DIP pins. I decided to redo that with cables instead to give me more mounting options.

I didn't have enough IDC connectors to put another set on the electronics board side of the cable, so had to solder the cable to the board.

The cable I had on hand had very thing conductors and not many of them. The cable I was using before was much better but had already fatigued and broken off some wires at the board. These thing conductors were sure not to last very long. So I decided the quickest solution was to add some mechanical support. See the piece of clear acrylic along the left hand edge of the board. This clamps the plastic part of the cable to the board and prevents movement (and fatigue) of the conductors as they enter the board.

In the close up you can also see a heat sink on the right hand edge.  This is for the transistor that controls the mash motor. This motor can draw up to 5 amps at stall, so the transistor can generate a little heat.

The other free standing TO-220 transistor is for the mains water solenoid. This only draws about 300mA so no heatsink required.

The orientation of the board was chosen so that I could get to the back side without removing it from it's mounting. This should facilitate easy mods or additions.

 3) Level probes in the pot.

Conductive level probes will be used to determine if there is enough liquid to safely power the heating element, and to determine how much water to initially fill the pot with.

The other conductive surface is the pot itself. Therefore the probes need to be insulated from the pot. To do this I used a cheap plastic chopping board.

I cut the corner off and mounted inside the pot.

The problem themselves are 1/8" 316 Stainless steel rod.

 Two screws come in from the outside and hold the rods in place.

4) Mains water solenoid. To be used to fill the pot with cold water at the start of the brewing process.

Decided to mount at the back, low and away from nearly everything. Hopefully this will prevent anything interesting getting splashed or sprayed should a leak develop.

Even tho there is a clamping diode across the solenoid driving transistor on the electronics board, I also included two clamping diodes right on the solenoid. I wanted to keep any EMF and the currents generated away from the MCU.

5) Shroud for the temperature sensor in the pot.

First up was to connect a DS1820 to some cable so that it would slide down inside the thermowell.
The a housing around the outside of the thermowell.

6) Lots of wiring. Not interesting enough to have a photo, but pretty much all the electronics and motors are now wired.

7) Adding a tap to the pot.

8) Adding limit switches to the Y-axis part of the crane. No pics so far.

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