Please bare with me, i haven't done anything major in electronics since college
I am a home beer brewer, and looking for a way to automate a part of the bottling. I have a bottle filler that only flows when the filler touches the bottom, and stops when it is touching nothing.
The concept is simple, lower the bottle filler into the bottle to the bottom and starts filling, and have a liquid sensor attatched to the filler. So when the sensor reads a full level, it lifts and the filling stops.
Does anyone have any experience with using a liquid sensor such as this?
Does anyone forsee any potential problems with this?
I see the scale solution being problematic with my solution.
In regaurds to fitting, i figured i could cut it down or ask them to custom make one for me, as their PDF states they will custom make a solution.
I suppose i could just always have a pair of metal leads that are proped right below the fill level and when they recieve signal when the liquid touches the leads because the resistance would change.
I havent done C/VB programming in a long time. Would that be difficult to code? Using a bi-directional servo and a pair of wire leads like that?
To lower the arm, until a signal is given from the leads, then raise the arm? It seems to be relatively simple coding compared to some of the projects that ive seen done.
You could use cap-sense. If there is a room for a drinking-straw down the bottle with the filler, you could use 2 small (narrow) stripes of copper-tape or alu-tape down the length of the straw on opposite sides (parallell plates + dielectric = capacitor). Connect wires from the arduino to the metal stripes and use the cap-sense library from the playground http://www.arduino.cc/playground/Main/CapSense
When the bottle fills, so will the straw and charging/discharging time will wary with the level of the liquid and thus you have yourself a level meter. this can mabie work on two foils on opposide sides of the bottle, but the distance is greater then and the arduino cannot support large current flow from the pins so the foil must be thin.
Beer bottles are not opaque. A light sensor is your best choice. Use a bright LED on one side and a phototransistor on the other with a decent gain. Shield it so ambient light doesn't bother it. Use an analog input, not digital, so you can calibrate it.
I'd also look at weight again, it's also easy, reliable, and cheap. Lots of real systems use weight for this kind of thing.
Float switches work, but not forever. Hollow plastic donut around the filler with some vertical something that trips a microswitch. Tricky to get reliable.
I'd worry about corrosion for the metallic strips using capSense. Wouldn't be FDA approved, for sure.
But level sensing is probably not so big deal
You can probably skip it:
The final fill level in the bottle is determined by the length of the center tube in the filling head. Beer will only fill the bottle until it reaches the end of the center tube, because it will flow back into the bowl through the center tube until it reaches its own level. Some machines will purposely over fill the bottles and then suck beer back out of the bottle to the correct fill height. After the bottle is full, it still has counter pressure present that needs to be relieved through what is known as a snift valve. Snift is a term used for releasing the pressure in the bottle in a controlled manner to keep the beer from over foaming. When snifting is complete, the full bottle comes off the filler and is transferred to a conveyor that moves the bottle to the crowning station.
Take a straw and cap off the bottom. Place a small magnet in the top of the straw. Put the straw in the bottle and find another tube slightly larger diameter than the straw to act a channel for the straw to travel through. Attach reed switches to the outside of the tube. As the liquid fills the straw rise and when the magnet hits the reed switch the pump shuts off. You could use 3 reed switches, first switch lets the Arduino know it's close to the top so maybe slow the pump down, second switch stops the pump and third could be a safety overflow switch.
b) Once the sensor has been used once, it will be wet, with droplets of beer adhering to it.
Neither makes any of the ideas above "impossible", but both are facts which will have to be accomodated
New idea 1: Are your bottles a standard volume? It might work to "pre-measure" the beer to go into the bottle in a different, intermediate tank, and when it has been filled, dump all of it into the bottle. This idea not far from one of the ways gasoline was sold to early motorists... they could see that they were getting what they paid for.
New idea 2: Insipired by Canon inkjet tanks... the ones for Canon printers with tanks separate from the print head.
In the bottom of the (clear... chipless, by the way... thank you Canon!) tank, there's a little prizm. A light beam is shot into it from outside the tank, bounces off of two surfaces, and re-emerges out of the side of the tank, to be "seen" by a sensor. This is what happens if the tank is empty. While it is full, the liquid outside the prism changes what the light does. Instead of reflecting internally, it passes out of the prism into the liquid. Neat! I bet your local ink cartridge re-cycling store would let you dig through their returned empties if you can't see what I mean, or duplicate the little prism by other means.
