RCTIME for 12 volt battery level monitor for Propeller

DavidM

Hi,

I have decided to not use the ADC chip, overkill/over complicated compared to RC Time method!

I have now updated my schematic to include RCTIME circuit to monitor the battery level back to the propeller via 1 x I/O pin, this will take up less space less I/O's and cheaper ( and also easier to code, I think?)

I am unsure of the values, but I have read some BS2 docs as well as the RCTIME docs for the Propeller and have come up with the following circuit V2.4

My goal is to return the voltage value of the battery to an accuracy of at least half a volt to the propeller. This will be monitored as needed ( i.e not continuously)

The components for the RCTIME circuit are in red text.

So my questions are..

Q1) Is this the right way to connect the RCTIME circuit?
Q2) Have I used the correct values for the two resistors & the capacitor?
Q3) If my spin application is controlling hi power loads ( i.e mosfet transistors/relays) via the 12 VOLT circuit, will the RCTIME values be different?
Q4) Do I need to have parameters/variables ( for conversion) in my code so that each circuit is individually calibrated?

Thanks

Dave M

Nick Mueller

> My goal is to return the voltage value of the battery to an accuracy of at least half a volt to the propeller.
> This will be monitored as needed ( i.e not continuously)

You won't have much luck with that setup. Lead-acid-batteries are the only ones where their remaining capacity can be guestimated from the voltage. But 0.5V resolution is not enough. Also, it is load-dependent. Try to get a data-sheet from your manufacturer and see what he tells.
Benchmarq made (they are now TI) nice battery monitors. There should be one that fits your needs.

Nick

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swrider

another option:

I am using lead acid batteries in most of my projects and use a voltage controlled oscillator (4046) to convert the voltage to frequency which can be read using PULSIN on·a stamp. I am just getting started with the propeller and hope there is a similar PULSIN function. 4046 example is on page 94:

http://www.parallax.com/dl/appnt/stamps/bs1Appnotes.pdf

Tracy Allen

The prop code will also need the math or the lookup table to calibrate the RCtime. You probably already have this reference:
www.emesys.com/BS2rct.htm#B_voltage
The equations there would apply, except the Propeller 1.65 volt input threshold is a little higher than the Stamp's 1.4 volts.

The layout of the wiring is important, so that the signal to the RCtime circuit will not be influenced by ground loops and other voltage drops. For question Q3, the voltage of the battery will also be influenced by the load, both continuous and instantaneous, so some averaging may be called for, but not I think different RCtime components. . Just keep in mind that any voltmeter across the battery is measuring its voltage under load at the instant. With the right setup, the circuit can read the battery voltage to withing 0.1 volt. I'm not sure what you mean by question Q4.

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Tracy Allen
www.emesystems.com