Hi,
I am trying to read quite low amps with arduion, using the shunt resistor. The problem is the amps are so small i get zeros on analog pins, so i am trying to amplify it with LM358 Amplifier Module (www.openimpulse.com/lm358-amplifier-module).
I have very simple circit now, just to try to find out how exacly it works. (Circuit attached).
If the module is not connected to the resistor, the arduino says something about 510 (+-10) which is half of the power source on the amp and that should be okay from what i understand.
But when i connect it to the resistor it shows these values (first is voltage on source, second is on the OUT of the amplifier):
The "amplified" values seems to be totaly indifferent to the source voltage or screwing the pot. And that makes absolutly no sense to me.
I would be very glad for any advice or tip how to solve this problem, or other way how to simply measure low amps with arduino. ¨
Thank you.
Additional info: The source is a sollar cell and i am trying to make a apparatus to measure its IV characteristics so in the end there will be additional potentiometer in the circuit.
Those amplifier modules are designed for AC amplification, see schematics from the link you posted, capacitor C2 in series with IN line.You need DC amplifier. You may try to get good result simply switching ADC to internal reference analogReference() - Arduino Reference
Thank you very much, somebody told me it could be used for DC but i wasn't sure.
Switching to internal reference did work for a first test, but for the second and others didn't, and i didn't change anything, so i really dont know what is up with that. I will deffinitly try it tomorrow again and we will see. Thank you anyway.
gumavkleci:
Thank you very much, somebody told me it could be used for DC but i wasn't sure.
Switching to internal reference did work for a first test, but for the second and others didn't, and i didn't change anything, so i really dont know what is up with that. I will deffinitly try it tomorrow again and we will see. Thank you anyway.
Well the website says its for DC, but the schematic shows an ac-coupled inverting amp so it couldn't
be used for DC.
LM358p(n)
Fonctionnement bien sous un circuit ft994k, mais le moindre faux contact, liaison geophone à l'ampli cause de véritable variante dans la stabilisation, voir des décalage stable de plusieurs centaines de points sur 1023.
Testé avec geophone verticale 4.5hz et 10hz horizontale, très stable (circuit sans anomalie) seulement 1 point de décalage sur 12h probablement causé par les condition extérieur nuit/jour.
Le circuit ft994k permet des réglages de stabilité, sensibilisation,
Pas tester avec condensateur, de plus il est parfois conseil une resistance entre led bornes du geophone.
Avec 2v5 de gnd au geophone 650 point environ sur 1023, en élevant la tension au geophone la sensibilité est plus élevé.
Le kit ft994k est bon sauf l'accès aux logiciel.. délaissé. Faire un programme simple sur arduino, mémorisé sur SD... http://www.iis-silva-ricci.edu.it/documenti/doc_download/1770-rilevamento-terremoti-con-arduino.html
Le circuit, de vue semble compliqué, mais il y a une partie indépendante pour un pcb accéléromètre .
Trimmer 50k (18k entre 5v et geophone, soit 2v5 au geophone), resistance 1k ohm, trimmer 1M ohms (500k sans trop savoir son influence sans condensateur).
