With our Dortmunder on tap, our Helles lagering, and our North German pilsner happily fermenting away in the Bavarian cave (temperature controlled refrigerator), it was time to get back to some construction work on HERMLET.

My work office was transformed into an electronics workshop allowing Leah to build the LCD interface board while I worked on a prototype board based on our picaxe 28x1 controller.

Leah working out component placement

Not much of a prototype yet - at least the picaxe is in place.

The completed LCD driver

The LCD driver board (P.H. Anderson design) takes a serial input and drives the LCD display.

The prototype to this point is quite simple. It gives a startup message and then waits for a button press. The control panel (shown below) is a resistive ladder with 14 pushbutton switches. Whenever a button is pressed, a voltage corresponding to that switch position in the ladder is sent to the picaxe and read on an analog to digital input. It works like a charm.

With our test code we were able to press a button and have the display show us which button had been pushed. This is not quite rocket science, but always a thrill to test another step in a larger project. It is a small step from here to add a temperature sensor and control a heating element - and then the first phase of HERMLET control will be just about complete.

Next weekend we will brew again, but should have time to make some further advances on HERMLET control.

Yesterday we completed our prototype control panel for the HERMLET project. Rather than build a final unit to put on the machine, we decided to iron out design issues by building a prototype as a step to a final product.

This was a good idea, because it allowed us to test and learn about a few things such as:

• the best way to attach panel artwork without destroying it
• how important it is to select the right components to simplify construction
• how easy it is to use a laminator for toner transfer compared to using a household iron.

Panel artwork

We laminated the artwork and glued it to the panel. We used forstner drill bits to cut 12.5mm holes for the switches and it seemed logical to use these to cut the holes on the artwork as well. We found that the artwork had a tendency to tear rather than cut neatly. A work around might be to glue the print to the laminate prior to laminating - but this seems messy. Another idea is to simply use paper, glue it to the panel and hopefully the glue will prevent tear-out. Yesterday we used a scalpel knife to cut out the larger holes. The 3mm holes for the LEDs remain a problem - how do we do that neatly?

(Maybe we need to find a leather punch of the right size ...)

Component selection

The switches we used were ones we already had. This seemed like a good idea. In earlier construction we soldered fly-leads from switches to circuit boards until I had the bright idea that we could direct solder to make things easier. The switches were designed with lugs rather than going through PCB holes - so the next bright idea was to solder them to the copper side. This might have been reasonable, except that it got to be a complex process dismantling the switches, soldering the tags onto the board at once, then reassembling spring and contact components and panel all at once. Not only was this difficult to do in terms of space, it means it is nearly impossible to solder the LEDs in place - something that really needs the panel in place first to set soldering depth.

We persisted despite these complications. We do not need to install the LEDs at this point, but the switch panel is now complete and operating as designed.

Laminator toner transfer

Yesterday we also visited our local Jaycar electronics shop and found some cheap and neat coloured switches that are true PCB mount. We even redesigned the circuit board and tested out the laminator process to transfer the toner onto the board. (See recent blog on PCB making for details). It was so simple to use that I don't think we will use an iron again.

Switch Panel Circuit

The circuit uses a resistive ladder to give a different output voltage for each panel switch. This means that a single ADC input on the microprocessor is all that is needed to decode a large number of switches.

For a good article and circuit diagram on this, see ADC keypad article.

Next steps

With the panel ready for work, a simple LCD setup and a breadboard circuit using our picaxe 28x1 means we can begin writing and testing the control circuit for HERMLET.

It's all about the beer ...

The Dortmunder export lager has been cold conditioning for a week now and was very promising out of the fermenter. The Munich Helles that we brewed a week ago is also coming along nicely. Our next brew will be a North German pilsner. We need to stock up on our lagers for the warmer weather ...