Using the Propeller to measuring Liquid Conductivity from the Applied Sensors T

edlikestoboogie

I was reading the parallax guide to Applied Sensors for the basic stamp. http://www.parallax.com/dl/docs/books/edu/AppliedSensors1_3.pdf I want to recreate the electrical conductivity lab described in chapter 5 on the Prop instead of the basic stamp2. Can I use the schematics on page 121 and 128, unchanged on the prop? Just the parts in the schematics involving the conductivity sensor and the LM555 timer. I know the prop is 3.3v and the BS2 is 5v.. So I suppose not. Can anybody shed some light on this?

StefanL38

hello ed_likes_to_boogie,

the DS1620 and the NE555 work as a special kind of analog-to-digital-converter (ADC)

The connection to the BS2 or the prop is a digital interface. A digital interface has two states:
1.) HIGH (+X Volt) and
2.) LOW (0 V)

You can connect most digital interfaces which use 5V to the propeller as it is described in the sticky thread
HOW TO SAFELY INTERFACE A 5V SIGNAL TO THE PROPELLER?

http://forums.parallax.com/showthread.php?p=585920

The circuit with the DS1620 or NE555 will still be supplied with 5V.

ATTENTION ! don't connect 5V directly to the prop-IO-PINs ! USE the circuits described in the tread above

The circuits might work at 3.3V too if the datasheet of the DS1620/NE555 has a supplyvoltagerange below 3.3V

The frequencies will change. But it should still work.
As 3.3V is a lower voltage than 5V there is no danger to expermintate with 3.3V

best regards

Stefan

Tracy Allen

Note that the part called for is the LMC555, with a "C"for CMOS, not the LM555 or the NE555. Only the CMOS version will work in that circuit due to the symmetric drive requirement. The LMC555 specifically from National Semi will work just fine on 3.3 volts, so you can use the circuit with the Prop directly with 3.3 volt power instead of 5 volts.

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Tracy Allen
www.emesystems.com

edlikestoboogie

Hey Tracy. The electrical conductivity sensor you created in the book, the one involving the two screws, could be recreated with the prop, right? I am trying to detect salt concentrations in a solution. I'm pretty sure you can use electrical conductivity (EC) to detect ppm concentration. Is there a batter way to sense solute concentration in solutions? Right now, I am short on time for a school project, so I am hoping the sensor you made with the two screws will yield some results.