ec & ph disconnect probes

Projects General Guidance
1

hello,

standing to what i read around ec and ph probes and circuit generate quite a few noise and it's suggested to use galvanic isulator to keep the read consistent.

now, my stupid question.

to save some $$ it's not just possible to add a control "pin" to shut down a probe while the other is taking measurement (of course 2 pins, one for ec the other for ph)

this circuits come with 3 pins, GND, VCC, gpio pin

(here a link for ph probe)

i read from a comment on this product

It's a bit complex, it involves a PNP and NPN transistor on the two leads to each probe, and I think I used 4 different GPIO pins to control it. I have the schematic, maybe I'll get around to posting a blog post on it and/or selling it as a product.

and

it would probably take 8 hours of work to make a tutorial, perhaps I'll get around to it one day. If someone pays me I'll get around to it a lot sooner.

that's a bit lame :smiley: lol

it would be possible to use a single TIP120 on each probe to block the GND?

something like
http://bildr.org/blog/wp-content/uploads/2011/03/tip120-lightbulb1.png

or the probe circuit will still generate some noise if i turn the GND off in that way?

2

It is almost always a very bad idea to parallel analog sensors! The issues are "induced" noises from AC power, induced voltage from RF transmitters, sunspots, etc .... bad idea.

The technology to use multiple analog sensors with one uC input is called analog multiplexing. To do it right, you need to be very good at analog circuits design and construction or you need a commercial built unit.

There are other ways to do this...

  • use different analog input pins on the uC
  • use a remote uC (maybe a $3 mini) off close to the probe and convert the analog to digital then transmit the digital signal to the host Arduino... via serial, SPI or I2C... example are available in the forum.

Personally, the best designs involve converting the analog to digital at the shortest reasonable distance where DC can be supplied for a remote Arduino.

Ray

3

i don't think that i get what you mean.

i know that add a mini uC will make the trick, but will make calibration a bit more complex.

all the data that i get will be feed to a ESPsomething for wifi transmission, and all config received from this uC

i can't just turn one of them "off" and leave the other "on" and do vice versa?
it's that the "multiplexing"?

i don't want to share a gpio pin, they will be on different pin. I was thinking that if i just "power off" one of them while the other operate, with a special extra control gpio port, everything will work, but probably i am wrong?

4

i can't just turn one of them "off" and leave the other "on" and do vice versa?
it's that the "multiplexing"?

It's called poor-man multiplexing ...
You get what you get ... unlikely to work correctly because of induced noise ... but, who knows. It is bad engineering practice, but it may work for you.

Ray