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Inside Mr. Coffee: Simple, effective design

Posted: 09 Jan 2015     Print Version  Bookmark and Share

Keywords:GUI  phenolic board  FR-4  transformer  microcontroller 

We had a basic Mr. Coffee 12-cup unit (figure 1)—at least 15 years old—that had seen better days. It has been relegated to the trash already. However, I couldn't let it go without a look inside. (The family discourages doing such forensics on new units, but it is OK doing so on those no longer in service.) So I did a quick teardown to see what made this unit, which was very popular in its time.

I always admire how designers and manufacturers of low-cost consumer products somehow manage to meet multiple, conflicting challenges. In the case of this unit, there's cost (it retailed for around ₹1,818.18 ($30), I think), performance, user features, cost, safety approvals, and cost. This unit did one thing and did it fairly well, and that's all it did. There was no Internet connectivity or fancy GUI—just a basic display showing time of day and some indicators for setting up brewing at a specified time.

Figure 1: Mr. Coffee's time may have come and gone, but it deserves a little attention in its final days.

The teardown was impeded at first by the special tamper-resistant screws used to hold the bottom cover to the main stand. The two holes in the screwhead demanded a special spanner-pin screwdriver. Since I didn't feel like ordering one, I resorted to one of my favourite tools: the X-Acto fine-tooth, thin-blade razor saw (figure 2).

Figure 2: The X-Acto razor saw is an indispensable tool for both delicate craft work and cut-through demolition. You can get blades with 24-54 teeth per inch from hobby suppliers.

This is a great tool for slicing through thin plastic, soft and harder metals, and other materials while leaving only a small kerf. Inside was a control board/user panel, heater element, and a few other items, plus connecting wires, of course (figure 3).

Figure 3: Not much inside: just electronics board and user I/O, heater, and safety-related connections.

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