Re: Dosing Control: Timing Your Grinder #2

How about a replacement mechanical knob timer from a Mazzer? Just dial in
the amount you need. Installation should be a breeze, just drill a hole and
wire it in. After all, differing bean densities will never allow a
consistent exact amount of grind for a particular time period. The variable
timer will also make it much easier on a day to day basis to adjust for
espresso, FP, single cup or full pot amounts. And then there's the whole
twisting the k-nob thing...

Greenbud
Hello, Mark!
You wrote on Tue, 20 Dec 2005 15:41:16 GMT:

MP> http://tinyurl.com/deume

MP> Someone suggested using a hockey puck type timer such as this:

MP> http://tinyurl.com/cr64c

MP> These would do a very good job and make the project much simpler. The
MP> reason why I didn't use one is because you can't cancel their operation
MP> once they start, and you'd have to figure something else out for pulsed
MP> operation.

MP> The prototype has the following elements:

MP> 1) 555 timer circuit. This circuit develops the time delay needed to
MP> keep the grinder on for the desired length of time.

MP> 2) 120V to 12V transformer.

MP> 3) Power supply circuit. This circuit takes a 12V AC input and
MP> converts it to a 5V DC output for #1. You could just use a 9V battery
MP> and delete this circuit and the transformer.

MP> 4) 10A solid state relay. The grinder is rated at 5A. I could have
MP> used less than a 10A relay, but I always like to design for twice the
MP> required current.

MP> 5) Project box and power cables going in and out.

MP> For item #3, I just bought a power supply kit from a guy on flea bay.
MP> It came with a circuit board and all the components which I had to
MP> solder on. It provides a DC output that's adjustable between about 5
MP> and 12 volts. I have it adjusted to 5V. I just used a short heavy
MP> duty extension cord cut in two for the power cord along with two rubber
MP> grommets going in and out of the box. All the other parts I bought
MP> from Allied electronics, which just happens to be based a few miles
MP> from my home. I had a little project PCB which I built the 555 circuit
MP> on. I tested it on a project breadboard before I mounted the
MP> components to the PCB.

MP> Here's a basic 555 timer circuit:

MP> http://www.aaroncake.net/circuits/relaytim.htm

MP> I used a 22uf Cap for C1. For R1 I used a 100K fixed and a 1 Meg pot
MP> in series. This combination allows for an adjustment range of 2
MP> seconds to about 30 seconds. It takes 8 seconds for my SJ to grind
MP> enough for 1 shot. Larger values for the Cap and resistors will allow
MP> for longer timing ranges. The circuit shows a 12V supply voltage, but
MP> the 555 will work fine with anything from about 3V to 15V, so a 9V
MP> battery works great. I didn't use Diodes in my circuit because I used
MP> a solid state relay. In the circuit, pin 4 is tied to the supply
MP> voltage, but in my circuit I put a button on pin 4 and then tied the
MP> other side to ground. This allows me to reset the timer by pressing a
MP> button (grounding pin 4).

MP> I also put a button across the control side of the solid state relay,
MP> tied to the supply voltage. I wanted to give the unit a pulsed
MP> operation. This function didn't work because apparently when you put a
MP> high on pin 3 of the 555, it triggers the timer. So my pulse button
MP> effectively triggers the timer just like S1. To fix this, I could
MP> install a transistor on the output (pin 3). This would isolate the 555
MP> from my pulse button. I'll save that for a modification at a later
MP> date. Right now I can get a pulsed operation by triggering the timer,
MP> then pushing the reset button.


With best regards, Greenbud. E-mail: xxx@xxxxxxx


.

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