thanks for your reply, the weighing scales intended to be used: http://www.adamequipment.com/uk/pdf/902.pdf
their accuracy is adequate. Using a switch wired direct to the solenoid valve I would calculate the lag time and in any case the accuracy of the fill should be +- 10g /10ml but one should remember that this apparatus is replacing manually controlled garden hose with the cylinder hanging on scales.
LCD display picked out of so many "20x4 Arduino LCD display HD44780 Blue LED Backlight" this would fit the bill as there are so many available for up to £24 the easier to develop with the better.
buttons: up, down, left, right, select, start, on/off power switch.
The most basic way for this to work is to set the target weight then press start to fill the cylinder. We could add a safety feature if no cylinder is in place but this could simply be a contact closure in series with the valve solenoid.
I would like to have the current weight shown on the display as the cylinder fills.
The most advanced development would be as follows, as different cylinders require differing quantities of water i would like to be able to select from a list of named cylinders ie, the model and type, the required weight is preset and ready to go. I would like this feature to be configurable using a menu system displayed on the LCD.
Also in the menu system could be a trim function for lag between shut of and actual end weight.
It would be great if you programmers could offer some feedback as to the complexity of the project. if you are interested in being involved and you feel that you could follow the project through completely please private message.
A full and complete specification will be settled upon with the developer prior to commencement of the contract.