I raised an issue sometime ago regarding voltage dividers and I had some great feedback and I have learnt lots and continued to self teach myself more since.
I have a question, and I have researched this, and I believe this will work, but would like to get a second opinion before I go spending money.
I have a voltage divider connect to an ADC1115, which is connected to the arduino. I do not want the voltage divider on all the time. I use differential readings as I do not share common negative. (I know there will be maybe comments regarding this, but it works!)
The voltage divider and ADC1115 circuit works.
My question... will the TLP175A work as a switch to turn on and off the voltage divider??
Please realize all circuits using solid state device have some leakage current. So, the answer is maybe, if your voltage divider can handle a bit of current.
Paul
I would use a reed relay to power the voltage divider only when you need it.
It probably will work when that 3-30volt source isn't connected to anything else.
It definitely will NOT work if that supply is outside the common mode range of the ADS1115.
It might even release the magic smoke and send it to silicon-heaven.
Leo..
The Adc and arduino are on a different Vcc and gnd than the differential readings I’m taking on the inputs.
This works fine. Or am I getting something wrong??
Maybe i need to research how a multimeter voltage reader works!
The ADC has absolute maximum input DC current 10mA. I think the setup is reasonably safe considering the 100k resistor. When the input diodes are conducting the resolution may degrade but OP claims it works well. I think it is safe to assume unconnected grounds are OK.
This circuit works find without connected negatives, I´ve been testing this for weeks now.
I´m really just interested if the TLP175A work as a switch to turn on and off the voltage divider? I understand there maybe resistance and voltage drops, but I can adjust in my calulations.
The factor is, if the battery is floating with respect to the 1115, then you risk having either of the 1115 analog inputs being pulled more than 5V above the 1115 gnd.
The potential divider ONLY prevents more than 5V BETWEEN the analog inputs.
The data spec is for analog input to gnd.
My voltage divider is setup so I will never have more than 3.2v at the analog pin. Hence the high resistors.
I will say I´ve blown a couple of ADC1115 when I removed the power to the ADC and left a battery connected to the divider. Thus powering the ADC though the analog pin. Not a wise move... This is why I need the switch!
Again thanks for the input. I´m learning electronics from new here! I´ve come up with some impressive solutions to my overall project, its just taking a bit of time!
grichfitz:
My voltage divider is setup so I will never have more than 3.2v at the analog pin. Hence the high resistors.
Your voltage divider is not referenced to the 1115 gnd, you will never have more than 3.2V BETWEEN analog pins.
Measure the voltage from 1115 gnd to each of the inputs used.
What is the battery connected to, what system?
Tom...
Tom,
Sorry. I do not understand what you are implying.
You understand I using differential readings between the analog pins? Not single reading between analog pin and gnd.
And as stated before the batteries are connected engines.
Anyway... I feel we’re going off track as this system has been tested and works. I’m just interested in the TLP175A.
I was confused too, but look at the OP's voltage divider, the few Ohms through the opto transistors should be negligible compared to the 112k divider resistance, with 30V minus the diode drop, the current would be 29.3V / 112k = 261uA flowing through 12k = 3.14V between A0 & A1. I think the OP's concern was the opto's behavior which should be fine as long as the LED current is correct.
