Hi there, thanks for the explanation. Do you mind
checking the circuit that I've simulated (as
attached).
By the way, with reference to the Point A in the
circuit, is it a must for me to include a low
resistance resistor at Point A before tapping the
voltage off the line? If it is a must, do you mind
explaining what is the purpose of doing so as I don't
seem to find any difference in having the resistor
there or not there.
Should I just use the voltage divider circuit in my
project? As I might face difficulties in supplying my
op-amp. Is it true that most of the supply voltage of
the op-amp is -/+15V? I will not be able to power it
up with my solar panel.
Thanks in advance...
--- rtstofer <> wrote:
>
>
> Many PICs will operate at 3.3V - I just used a
> 16LF628A at this
> voltage quite successfully.
>
> A voltage divider of, say, 2 is quite simple: use
> two 1K ohm
> resistors in series. Put one end of the string at
> ground, the input
> voltage at the other end and the center point will
> be 1/2 of the
> input.
>
> Want divide by 3? Put the input into a 2K resistor
> (or 2 1K
> resistors in series) use the same 1K resistor to
> ground and measure
> at the upper end of the 1K, just like before.
>
> Now, here's where it gets ugly: The input impedance
> of the A/D
> converter is in parallel with the lower resistor,
> reducing its value
> by probably 10%. To get a more accurate solution,
> you may need to
> increase the lower resistor to 1.1K. You can do
> this with 2 2.2K
> resistors in parallel.
>
> Of course, the proper way to do this is with an Op
> Amp because the
> output impedance of the Op Amp is quite low and the
> input impedance
> of the A/D converter won't affect the accuracy of
> the division.
> --- In , "Allan Lane"
> <allan.lane@h...> wrote:
> >
> > I assume you will be using a low-drop-out
> regulator (like a 3940-
> 5)
> > to regulate the output of the solar panel?
> >
> > The 'drop-out' voltage (0.5 volts for the 3940) is
> how much
> voltage
> > over the desired one you must produce, for the
> regulator to work.
> >
> > Never having done what you are trying to do, I'm
> not sure of the
> > voltage range of the PIC. It does have a
> 'brown-out' setting,
> though.
> >
> > --- In , "devonsc"
> <devonsc@y...> wrote:
> > >
> > > First of all, thanks a lot for everyone's
> kindness in guiding me
> on
> > my
> > > doubts before this. Would like to ask regarding
> the following
> > matter:
> > >
> > > Firstly, the voltage output of my solar panel
> varies from 4V to
> 10V
> > > (Will not exceed 10V). I intend to shut the PIC
> down if the
> output
> > of
> > > the solar panel is lower than 4V. Apart from
> that, I intend to
> > > power-up my PIC using the power directly from
> the solar panel.
> > >
> > > About reading voltage value using ADC, is there
> a way where I can
> > > scale the read down the values from the solar
> panel output?
> > Something
> > > like: What ever reading value I obtain from the
> solar panel's
> > output,
> > > I make sure it is being divided by 2 before
> being applied to the
> ADC
> > > input of the PIC using a voltage divider. If
> yes, do you guys
> mind
> > to
> > > guide me in this simple circuit? I tried doing
> some simulations
> to
> > tap
> > > the voltage from a source and divide it to
> obtain a half of
> through
> > > simulations but fail :(
> > >
> > > Meaning, overall, I intend do the following: By
> having 2 ADC
> inputs,
> > > a.) one would be an input of a "limited to 5V
> input". At this
> point,
> > > if the PIC reads a value of lower than 4V, I
> shut off the PIC.
> > >
> > > b.) another would be an input of a "voltage from
> the solar panel
> > > divided by two". This will be the one to control
> my PWM duty
> ratio.
> > >
> > > By the way, the duty ratio will be used to
> control my on/off of a
> > > MOSFET and I need approximately 16mA to turn it
> on. Would like to
> > > confirm, about this: Does it mean that if the
> voltage used to
> power-
> > up
> > > my PIC is 4V, I will obtained an output current
> of approx. 20mA?
> > > Whereas if it is 3V, it will be approx. 15mA?
> > > _________________
>
>
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