Keurig Coffee Maker Automatic Filler Circuit

This is a really neat project, it makes the Keurig even easier to use. It also prevents a common problem that occurs with my model of machine (B40): sometimes the float on the reservoir doesn't register and thinks it is empty.  I just make it fill, just before it is supposed to register as empty.  Here is the unit in action:

There are three main parts:
1) Plumbing
2) Electronics
3) Float sensor
and the last section (4) contains some notes on testing

Don't be intimidated, these are not that hard, but you do need some electronics experience to make it easier.  If you feel you can't trust your soldering skills, it might be a good idea to use a chip socket for the 555 chip that we use.

Generally, the design works with the fact that the water reservoir uses a magnet (right side of closeup picture) to sense that it is empty.  We will use a reed relay, which can be activated by this magnet, to initiate a fill cycle.

You will need to read through the whole process to be assured you can do all of the steps, and that you have everything you need.

Step 1: Plumbing

This step requires:

-shut-off valve
-electric valve ( search Ebay for 12V valve 1/4", make sure pressure rated.  example http://www.ebay.ca/itm/12V-DC-1-4-Electric-Solenoid-Valve-Air-Water-Diesel-/180784450198?pt=Pneumatic_Hydraulic_Valves_Parts&hash=item2a1797ca96)
-fittings to connect hoses to electric valve (thread to hose adaptation as required), with Teflon fitting tape, or paste.
-high pressure 1/4" (cloudy white color) hose
-1/4" clear hose
-bushings / collars for hose ends
(all items above at home center except electric valve)

By far the most expensive parts in this step are the two valves (shut-off & electric), which are about $10-15 each.

You will need to start by putting in a tap from an existing water line.  Make sure you turn off the water and relieve the pressure before installing the valve.  I would NOT buy a cheap 'saddle valve' , the kind that pierces the pipe by itself.  I went through a couple of these before giving up.  They are not worth it, and even illegal in some places because they can leak terribly!

Since the hose between this valve and your electric valve will be under pressure, I would get the (cloudy) 1/4" higher pressure hose and not the clear stuff.  After the electric valve, I would use the 1/4" clear hose, as it is easier to work with, and not under pressure.  You will need some of this anyway, to insert the level sensor we'll be making later in step 3.

It might be an idea to buy an ice-maker kit (which you would otherwise buy for your fridge), which includes the shut-off valve, hose and some other stuff.  I realized this after I bought all the other parts piecemeal.

Step 2: Electronics

The electronics are not too difficult, especially if you are familiar with 555 timers.  if not, you should be able to replicate the circuit provided without too much trouble. I bought an enclosure with a matching prototype board to put all the parts onto (see link) for about $14, but I'm sure there are cheaper alternatives.  This is by far the most expensive part of this section.  The rest of your parts should be way less than $10. Don't be afraid to buy at least double parts just in case, like the chip for example.

I should give you a link for the reed switches here, since it took a while for me to find the right ones. Buy a bunch, they are glass and can be very sensitive to breakage if you bend them too roughly, especially after you have soldered wires to them.  Heck, they are about 65 cents each, so buy 5 or so!

It might seem silly, but putting a terminal block (like the green block shown, ideally with 6 positions for this project) on the board is the best thing you can do.  Assembly, troubleshooting and installation is a breeze with it, and can be a nightmare without it.

I hope you have a 12VDC wall wart from an old electronics device.  Otherwise, they have a plethora of these at places like Value Village.  You could also buy one at Mouser/Digikey/etc. if you have to.

I will not help you find the rest of the electronic parts, as found in the schematic pdf below, but you should be able to find everything you need at Mouser, Digikey, etc.  I have a preference for Mouser, since they ship anything for $20 to Canada with no duty or taxes, and if your order is over $200 (although certainly not in this case), it is free shipping.  If you are in the US, you are even better off.

NOTE! It took a while to figure out, but it is very important to put a 1N4007 or equal diode (anode to 0V) across the valve which is not shown on the the schematic.  For me, the electrical inrush of the valve fed back to the 555 chip and messed it up.

Step 3: Water Level Sensor

Perhaps the cheapest section, but the most finicky, is the sensor part of this project.  If I won the Shopbot contest, my first project would be a sensor bracket, but alas, here we are...

What I did was solder two lengths of wire on each end of the reed switch, run it through a length of clear 1/4" hose, and insert it into the reservoir:

a) solder the reed switch carefully, without clipping the leads, soldering close to the ends of those leads with the pieces of wire (I split speaker wire in half).  Keeping the leads long allows for more bending without damage to the (glass) reed relay.  Both wires will need to reach your control box, so make sure it is long enough.

b) fish the wire through 1/4" clear hose, long enough to loop to the bottom of the reservoir and back up. I used an old metal coat
hanger and pulled the wire through, but any stiff wire will do.  Pull until the reed is halfway through the hose.

c) carefully bend  a loop at the end where the relay is, and test activation by the reservoir magnet, with a multimeter for continuity.  you will need to twist the reed relay, as it is certainly a directional device.  One side of the reed relay will work best.

d) bend and fasten the loop for optimal performance, with wire ties, and you can also stiffen the straight parts with a section of the coat hanger you may have used. Furthermore, employing coat hanger pieces into the hose at the upper part allowed me to make hooks to latch to the top of the reservoir.  

I also ended up using a short piece of thicker hose (you can see in the picture) as a spacer, to make sure the reed was nice and close to the magnet, without impeding the magnet's movement. You can also combine the filling hose with this assembly.  You will have to fart around a bit to get it right.

e) use tape to fasten the assembly to the outside of the reservoir.  Electrical tape worked for me, as long as I cut it with scissors or a knife.

Step 4: Testing

The schematic allows for a range of 0.5 seconds to 52 seconds, and should be adjusted to your water pressure.  It would be a good idea to have a pail or basin nearby so that you won't spill water all over the place.

You can just short the reed terminals with a piece of wire, to test the timing without water.

The timing I set allowed for two fills by the circuit, just as a precaution.  You should also close the shut-off valve if going away on vacation, or not using the machine for prolonged periods of time.

NOTE! It took a while to figure out, but it is very important to put a 1N4007 or equal diode (anode to 0V) across the valve which is not shown on the the schematic.  For me, the electrical inrush of the valve fed back to the 555 chip and messed it up.