cheap displacement probe??


Thread Starter


I'm currently developing an invention that will require a small displacement probe to measure 3-4 inches of range with no need for a lot of accuracy (its not a professional or scientific application). The main problem is that it has to be no more than about $30 when purchased in bulk, preferably a good bit lower than that. I would like it to output to a small LED screen. Does such a design exist? Is this something an intelligent person as myself could possibly hope to build? Thanks for reading, hope you can help.

- Jim
Maybe use a potentiometer with a lever on the shaft with a weight or spring to return it to the home position. The lever should probably be 4-6" long.
Steve Myres, PE
Automation Solutions
(480) 813-1145
Does it have to measure the range? At that cost don't think you can do it. However there are some cheap PVC float single point by Gems. I think model number is LS7.
just a suggestion: buy a household digital bathroom scale and take it apart...

some models have an "encoder" type arrangement... the weight (applied as a linear motion) turns a slotted disk... a photosensor shoots a beam through the slots... the slots are counted and the corresponding weight is shown on an LED display... this type may NOT meet your needs...

other models have an LVDT (Linear Variable Differential Transformer) arrangement... the weight (applied as a linear motion) slides a slug inside a variable transformer coil... the varying voltage output is shown as a corresponding weight on an LED display... this type might be close to (if not exactly) what you're looking for...

sorry I can't offer any specific brand or model numbers... it's been many years since I ran across this knowledge...

good luck...

Curt Wuollet

Sounds like a good place to use a pot and string linear to rotary conversion. And there are good "digital pot" encoders available at low cost if you wish to avoid A/D conversion. If you make the spool on the pot about 5" in circumference, it would use the whole range. Or, I saw a clever low cost idea to use a piece of timing belt bonded to the member as a rack with a matching pully on the pot.
Low cost, fairly precise, and OTS.