## RE: [Electronics_101] Re: question

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• Kerim, I think the circuit could be modified to do what you want. Rather than use comparator C , you would need an amplifier with sample and hold
Message 1 of 64 , Jul 1, 2012
Kerim,

I think the circuit could be modified to do what you want. Rather than use
comparator "C", you would need an amplifier with sample and hold
capabilities. The monitor should work with any reasonable load on the
battery so could run continuously. I played with this idea back in 1973 when
I developed an in-circuit ohm meter.

Rick

-----Original Message-----
From: Electronics_101@yahoogroups.com
[mailto:Electronics_101@yahoogroups.com] On Behalf Of Kerim F
Sent: Saturday, June 30, 2012 1:31 AM
To: Electronics_101@yahoogroups.com
Subject: [Electronics_101] Re: question

--- In Electronics_101@yahoogroups.com, "Rick Sparber" <rgsparber@...>
wrote:
>
> I have posted two articles in the last few weeks that deal with analog
> circuits. The response has been underwhelming. Not a single comment.
> Are there any analog circuit designers left on this BBS?
>
>
>
> Rick
>
> rgsparber@...
>
> rick.sparber.org
>

Your work reminds me an old small project I was working on but I didn't
finish it. I liked to measure approximately the DC internal resistance of a
car acid battery by measuring the small voltage drop on its terminals for a
Let us assume the battery voltage is 12V and its internal DC resistance is
about 5mR. If the load current (actually a current pulse with a proper short
period) is 10A (via MOSFET and current regulator) the voltage drop would be
50mV. In this case, the ratio of the high side voltage is 11.95/12=0.996.
This ratio depends on the battery size and its age, for a few.
I didn't have time yet analyzing attentively your interesting circuit so I
am not sure how much it may be related to the high side voltage measurement
that has a very small difference to be measured even approximately. After
all, the project is just to build a tool for comparing the strength of some
big batteries under test. I am afraid it will need a few LEDs (instead of a
display for simplicity).

Kerim
• Kerim, It is funny what consumers latch onto for importance. You work hard to get the circuit board down by 0.1 and then have to bolt it to a block of steel
Message 64 of 64 , Jul 8, 2012
Kerim,

It is funny what consumers latch onto for importance. You work hard to get
the circuit board down by 0.1" and then have to bolt it to a block of steel
to get any credibility. Going with a simple resistive load current should
work fine since delta Vbattery is small.

I look forward to hearing more.

Rick

-----Original Message-----
From: Electronics_101@yahoogroups.com
[mailto:Electronics_101@yahoogroups.com] On Behalf Of Kerim F
Sent: Thursday, July 05, 2012 7:10 PM
To: Electronics_101@yahoogroups.com
Subject: [Electronics_101] Re: question

Rick,

In my free time (since I work on other projects), I started designing its
analogue part on LTspice. I will include the digital part using voltage
sources having each a proper timing list. Since AT89C2051 is an old and
simple MCU (20-pin), it doesn't have an ADC feature. Instead, it has an
internal comparator and its two inputs are P1.0 and P1.1 (its output is
P3.6, an internal flag). So when I need measuring a voltage, I measure for
example the charging time of a capacitor till its voltage reaches the
measured voltage. Obviously an external opamp or comparator can also be
used.

You are right about the display; a number looks more professional. After
all, implementing either one is done mainly by software. The irony is that I
noticed most consumers are impressed more by the size (if not the weight
too) if it is larger ;)

To reduce the circuit, I removed the load current regulation. So the current