Hi all,

I am in the process of designing an automatic nutrient/water mixing system that is to be controlled by an SMS controller..

I have sourced a 8 input / 8 output SMS controller and for now I am designing the 1st stage for use with the controller which is..

a 50 gallon (190 litre) black plastic water tank with a hose attached to the side of it going through a normally closed solenoid the valve will be opened by the controller (attached to an output) ...where the water comes in I will have a ball valve with float to shut the water off when it gets to a certain level then I will close the solenoid valve

2 x float switches which will be attached to 2 inputs on the controller this will notify me when the tank is full (I will turn off above input solenoid/valve) and notify me when the tank is empty (know when to refill)

The problem I have is I need to be able to mix a specified amount of nutrients into the tank..they will be mixed by a pond pump in the bottom of the tank that I will turn on/off via another output on the controller. I need to be able to deliver 300ml of nutrients from 4 x containers upon activation again on the outputs of the sms controller (4 x liquid vessels) I have looked at ways of doing this and it could be done by using solenoids that deliver a certain amount of ml per minute but I need it to be a lot more acurate i.e exactly 300ml each time I make the circuit...im wondering if anyone has any experience with such things?

Thanks

 

I believe one way this is done is to use a shot tank. So you fill the shot with the required amount, treating the filling operation much the same as your large tank, and then you dump the shot tank into the larger vessel. The control scheme is essentially identical as for the large tank, just much smaller. Positive displacement piston pumps are also used, with each shot being like a big syringe.

 

Thanks for the reply..

Im wondering if using a peristaltic pump might work http://cgi.ebay.co.uk/PERISTALTIC-D...8?pt=UK_BOI_Restaurant_RL&hash=item1e5c0398ce

It would have to automatically turn itself off after a set amount of minutes on the basis it delivers 34ml per minute i.e 300ml would equal 9 minutes this might be a bit hit and miss though as it would need some kind of timed switch/relay that will turn it off after the exact amount of time?

........maybe a timed relay like they have in cumunal lighting systems I fitted one of these many moons ago when an inductive lighting load kept burning out conventional timers. I reckon if I put the sms controller across the trigger side of the relay set for 9 mins it would engage the 230V pump then turn itslef off again..would need some testing to see how acurate the peristaltic pump is though

 

They can be quite precise. That technology is used in labs for repetitive delivery of precise volumes. If I recall, you can control both the speed of the pump and its duty cycle.