Help designing circuit for stamp module I need help designing a circuit that will tell a stamp module to turn or off a pump based on TDS levels in water. What has happened is that the main unit has only on 1 IN left but I need to be able to create a range of TDS to compare. Here is the situation: A TDS monitor checks for levels of Total Dissolved Solids in water. The monitors that I am using have an alarm circuit that activates when TDS levels are >= the set parameter. The alarm is a normally open relay. What I need is to use 2 monitors together to create a “range” of TDS that the pump will activate for. I.E. I want to pump to be active only when the TDS is above 50ppm and below 75ppm. My novice electronics thinking is that with the correct combination of transistors I can create a circuit that will send 5v to the Stamp when the TDS reaches 75ppm and 0v when the ppm is less than 50ppm but not send 5v until the ppm is greater than 75 again. Therein lies the crux of the problem. Software wise, this is a no brainier, but as stated I have only 1 IN left to use. In PseudoBASIC this is how it would look TDSLoop TDSLowRange = 50 TDSHighRange = 75 TDS1ppm = Reading of TDS 1 probe TDS2ppm = Reading of TDS 2 probe TDS1Alarm = OFF *Boolean for state of alarm TDS2Alarm = OFF *Boolean for state of alarm Pump = OFF *Boolean for state of pump If TDS1ppm >= TDSLowRange then TDS1Alarm = ON If TDS2ppm >= TDSHighRange then TDS2Alarm = ON If ((TDS1Alarm = ON) and (TDS2Alarm = ON)) then Pump = ON *Send 5v to Stamp IN While Pump = ON If TDS1ppm < TDSLowRange then Pump= OFF End While Pump = OFF *Stamp in 0v Goto TDSLoop End TDSLoop Only I need to do this electronically. Please help!
Neither. The only usable output is the alarm which is a normally open relay. The TDS probe connects to the TDS module which converts the readings and houses the display.
Are you sure you can't multiplex some of the other inputs and outputs to give you some room for two inputs on the STAMP?
I don't believe multiplexing is an option. I will look into it. However, I may have made the explanation a bit too complicated. The bottom line is this: The pump needs to turn on ONLY when both relays are closed ( the TDS level exceeds both set levels) and turn off ONLY when both are open ( the TDS level is below both set levels).
ive been trying to work out what you want from the circuit. im confused by your first and last posts... do u want to create a range in which the pump should turn on or something else?
From my reading of it you need some logic before you get to the stamp. If you put an XOR gate with the two alarms connected as inputs then when the 50ppm sensor goes off the output will become a logic 1. When the 75ppm sensor kicks in too it will turn off the output. When both sensors are off the output will also be low. You can buy an XOR logic gate from any of the major suppliers.
If you look up a manual for staps you notice that they have analoug pins, how does this help? On ALL alarm outputs (normally open relays?) place a different value risistor and connect in series so that all alarms are closed only by the risistors. NOw heres were it may get confusing When an relay is triggered a risistor is bypased by the contacts reducing the overal value.this means that multiple switches can be connected to one pin. If im just confusing you ill try to drw out a circuit diagram.
wow i feel just like i did when i opened a book and it was in russian lol. what exactly is a stamp module?
Thanks for the vote of confidence but its not mine, its printed in the stamp manual. Stamp Manual Page 157
Thanks to all for the help. As it turns out, there were 2 I/O's left, not one, so problem solved. The guy that built the proto did not add the last I/O to the daughter board. So a little soldering and viola problem solved.
