Infus-o-matic

A very useful contraption to make the perfect tea/infusion.

I love good quality tea, infusions &co. but one of the thing I noticed is that when I'm at the pc, even using a pc-based timer, often happens that the infusion time did not match my expectations, and this could be quite critical.

In this phase I was looking online for some ispiration, a lot of projects came up but none that I really liked, so as usual I decided do rethink the whole thing and learn during the process of making the perfect one.

A solid base for a cup that on average has an height of 10cm, water height of about 6.5cm and a diameter of 10 to 12cm, the whole thing must not tilt in any unintended way.

An average teabag measures about 5cm with a 14cm string; a "ball" metal version is 5cm with a 11cm chain.

The total for the base is 20 by 12 cm, the arm has an inner arc of 8.5cm and an external of 10cm, no straight lines because "phishing" the teabag this way is more aestetically pleasing and also reduces the weight, increasing the movement range.

The buttons are placed to be easily reachable and on a plane to avoid any lateral pressure.

The weight of a wet teabag could get to 10g, a wet metal ball even to 30g. I had already some mg996r with a stall torque of 11kg/cm that are definitely overkill, did a bit of research and came up with a minor version, the mg90s that has a maximum of 2.2kg/cm, so for a 12cm arm results in 180g/150g(depends on battery charge), metal gears and cheap, has no mechanical stop.

The electronic is very simple, the programming depends of what you intend to do, in my case 4 buttons, recall memory, subtract minutes, add minutes and start/stop.

A pic16f88 is used, along with a piezo buzzer for sound and a bunch of leds, not even worth designing a pcb, I've straight used a leftover piece of protoboard.

Press the power button(right) to wake up the pic16f88 and start the program, a startup sound is played, the arm rises, a default 1min is loaded on the minutes(green) bar, the time is in binary format to allow up to 15 minutes(and because I love using it anywhere XD) that should be enough in most cases, tea ranges from 2-5min, light infusions 7-8min and ginger, chamomile etc. can go up to 15min, never used more than this.

If you don't take any action(accidentally pressed button) it will turn off after a couple of minutes, warns halfway.

Press add/subtract to adjust time or the memory button(left), in this case there are 2 positions(yellow leds 1 or 2 lights up), long press to memorize the new preset.

At this point pressing again the power button begins the cycle, the red led lights up, the teabag/ball is slowly(takes about 15 seconds) submerged to allow hot water to soak and creates micro-waves in the water due to the servo motor.

After the first timer ends, the arm slowly rises again, a first approach to keep it in position was to use a counterweight and cut off the power to preserve the battery but in the end it doesn't worked very well and for heavy weights even worse, the red led turns off.

Then there are 2 cooldown timers pre-calculated for a total of 15min, the yellow leds are used, halfway the left turns off, when complete, also the right turns off, a final sound is played and the green leds make a moving pattern.

Remove the teabag(of course) and press the power button to turn off eberything and lower the arm to the rest position.

You can interrupt anytime the cycle, in this case the green led indicates the end but also the red led turns on if still in the immersion phase, indicating an "error" occurred, else it just goes to the final phase.

The time can also be adjusted before or after the immersion started, the cooldown is changed accordingly and of course cannot be changed but only skipped.

Initially a little clothespin were used to keep everything in position, now it is integrated in the arm(see pictures), along with an enhanced notch, even for the heaviest metal ball.

When battery gets low if you forget to recharge, strange thing happens but adding a small led that reminds you a little earlier should work just fine; if you're using unlike me a microcontroller with some spare pin, you can also use one of them to sense the voltage.

The minimum acceptable voltage in my case is 3.6v but I decided to put the threshold a little higher just to be safe, about 3.65/3.7v, the circuit exceeded my expectations and is fairy accurate, the total power consumption now when idling is about 5.1mA and should last at least double the time I usually recharge(1month vs 2 weeks).

After the last software upgrade the arm supports up to 50g of weights without problems but the servomotor uses more energy, a counterweight also was not an option, what could I use? A simple spring! it compresses nice during the arm swing and when it is in the upper position helps supporting the effort.

The previous counterweight wasn't working as expected because it was fixed to the arm and when in parking or lowered position there were some issues of unintended rotation, the spring quite worked but in some occasion caused the arm to move and needed to be set for a better free rotation on the hinges.

This solution is almost perfect, because when lowered or in parking position, the thread forms a "reversed V" and the weight is on the servo and pulley, when the arm is lifted, even with a heavy weight, the counterweight perfectly balances it and since it touches the ground it's also good for any lighter weight such as a teabag.

I initially thought of an elastic band that could be moved to predetermined tension marks but it would not be automatic even though slightly more elegant.

A further improvement could be a reallocation of the fixture point for the thread because it is slightly in the way only when inserting the teabag but I think that I can deal with it for now.

Sorry for the lacks of documentation but I thought of writing an ible after making this, anyway it should be intended to inspire for your own creation because everybody has different needings, some could prefer an lcd display or different types(7segments or others leds), an analog control knob or touch buttons I have chosen my own reason not to use them(step 1).

Even after building it, it took at least 3 major revision of the software, now I'm really satisfied on how this came out, the battery also lasts more than I expected(about 2 weeks between charges that is more than enough).

Enjoy