TAPR Digest (3/5)
Igor Buslayev
=== Begin m_006532.mes ===
From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: RE: PCsat Endangered
From: Jeff King <je...@aerodata.net>
Date: Sun, 18 Jan 2004 15:08:02 -0500
X-Message-Number: 15
On Sun, 18 Jan 2004 11:44:38 -0800, Scott Miller wrote:
>And to keep this thread marginally on-topic, I'm thinking of putting
>a battery voltage monitoring circuit in my tracker. What I've come
>up with so far is just a two resistor voltage divider, with a tap
>going to a spare A/D input. The A/D is internally referenced to the
>MCU's supply voltage, which comes from a regulator, either a 78L05
>or AN77L05. Is this the accepted way to do such a thing, or is
>there a better approach, keeping in mind that I don't have the
>ability to change the A/D reference voltage?
It is certainly the easiest way. Bear in mind, that you'll end up getting a
compression of the readings, since you'll only be able to read between
+5volts and whatever the resistive ladder tells you "255" is. Lets say you
use a 3:1 divider, so 15 volts at the battery would give you +5 volts at the
A/D/ input (255). So, the trusted range would be a count of ~85 to 255 (+5 to
+15) not taking into account any drop across the regulator.
You could expand this (say to read 10-15 volts full 255 range) by using a
op-amp to scale and offset the voltage. Below 10 volts would be a -0- and
over 15 -255-.
I suspect the following idea would work for either method, but you could
actually use the A/D reading to start and stop the radio/GPS. When a vehicle
is running, the voltage should be about 13.8volts, when not running, around
12 volts.
-+--------------------------------------------------------------------
Subject: Re: Attended vs Unattended
From: Derek Koonce <de...@dkoonce.com>
Date: Sun, 18 Jan 2004 12:28:42 -0800
X-Message-Number: 16
Since lower-case is not valid, Then what about just adding or
subtracting 1 from the character code, thus instead of an 'N' use a 'O'
or 'M'. Keep the code as it is for now, but say that the current code is
for inactive stations. Use the shift to signify an active station. Then
use the time-out period to change to the inactive state.
(I'm not much into the detail of the system, but this was just a thought.)
Derek Koonce
KE6JTP
-+--------------------------------------------------------------------
Subject: RE: PCsat Endangered
From: Derek Koonce <de...@dkoonce.com>
Date: Sun, 18 Jan 2004 12:32:39 -0800
X-Message-Number: 18
Jeff King wrote:
>>And to keep this thread marginally on-topic, I'm thinking of putting
>>a battery voltage monitoring circuit in my tracker. What I've come
>>up with so far is just a two resistor voltage divider, with a tap
>>going to a spare A/D input. The A/D is internally referenced to the
>>MCU's supply voltage, which comes from a regulator, either a 78L05
>>or AN77L05. Is this the accepted way to do such a thing, or is
>>there a better approach, keeping in mind that I don't have the
>>ability to change the A/D reference voltage?
>
>It is certainly the easiest way. Bear in mind, that you'll end up getting
>a
>compression of the readings, since you'll only be able to read between
>+5volts and whatever the resistive ladder tells you "255" is. Lets say
>you
>use a 3:1 divider, so 15 volts at the battery would give you +5 volts at
>the
>A/D/ input (255). So, the trusted range would be a count of ~85 to 255
>(+5 to
>+15) not taking into account any drop across the regulator.
>
>You could expand this (say to read 10-15 volts full 255 range) by using a
>
>op-amp to scale and offset the voltage. Below 10 volts would be a -0- and
>
>over 15 -255-.
>
>I suspect the following idea would work for either method, but you could
>actually use the A/D reading to start and stop the radio/GPS. When a
>vehicle
>is running, the voltage should be about 13.8volts, when not running,
>around
>12 volts.
If it is in the car, just find a voltage that will come on when the
ignition is turned on and use this as a signal. Why bother monitoring
the battery voltage since a no-load battery can be above 12V.
Derek
KE6JTP
-+--------------------------------------------------------------------
Subject: RE: PCsat Endangered
From: "Scott Miller" <sc...@3xf.com>
Date: Sun, 18 Jan 2004 12:47:52 -0800
X-Message-Number: 19
>It is certainly the easiest way. Bear in mind, that you'll end up getting
>a
>compression of the readings, since you'll only be able to read between
>+5volts and whatever the resistive ladder tells you "255" is. Lets say
>you
>use a 3:1 divider, so 15 volts at the battery would give you +5 volts at
>the
>A/D/ input (255). So, the trusted range would be a count of ~85 to 255
>(+5 to
>+15) not taking into account any drop across the regulator.
Yeah, I understand. A 3:1 divider would give a resolution of about 0.06
volts, and really I'd be happy with 0.1 volt resolution. And I'm pretty
sure I can squeeze two more resistors onto the board, but there's no way I'm
putting an op amp on there. My only concern is that the standard regulator
setup is good to 35 volts, so someone might exceed the 15 volt limit. I
think I can address that by just making it optional, like the temperature
sensor, and indicating that it should only be used with a 15 volt max
supply.
>I suspect the following idea would work for either method, but you could
>actually use the A/D reading to start and stop the radio/GPS. When a
>vehicle
>is running, the voltage should be about 13.8volts, when not running,
>around
>12 volts.
Good idea... I'll have to remember to try that.
Scott
-+--------------------------------------------------------------------
Subject: RE: PCsat Endangered
From: "Spider" <spi...@rivcom.net>
Date: Sun, 18 Jan 2004 13:50:49 -0700
X-Message-Number: 20
>If it is in the car, just find a voltage that will come on when the
>ignition is turned on and use this as a signal. Why bother monitoring
>the battery voltage since a no-load battery can be above 12V.
>Derek
>KE6JTP
Hi Derek!
Naw.....I do not like the idea of that sort of ckt....because you may want
it on in an unattended vehicle.
I suppose the idea is to just not kill the battery.
Jim, WA6OFt
-+--------------------------------------------------------------------
Subject: RE: PCsat Endangered
From: "Scott Miller" <sc...@3xf.com>
Date: Sun, 18 Jan 2004 12:50:25 -0800
X-Message-Number: 21
>If it is in the car, just find a voltage that will come on when the
>ignition is turned on and use this as a signal. Why bother monitoring
>the battery voltage since a no-load battery can be above 12V.
I'm adding the voltage monitor mainly for applications like high-altitude
balloons, where knowing how low your battery is getting might be important.
What Jeff suggested is just a way to put that same (very simple) circuit to
use for another purpose.
Scott
N1VG
-+--------------------------------------------------------------------
Subject: Re: Attended vs Unattended
From: Steve Dimse <k4...@tapr.org>
Date: Sun, 18 Jan 2004 15:51:21 -0500
X-Message-Number: 22
On 1/18/04 at 12:28 PM Derek Koonce <de...@dkoonce.com> sent:
>Since lower-case is not valid, Then what about just adding or
>subtracting 1 from the character code, thus instead of an 'N' use a 'O'
>or 'M'. Keep the code as it is for now, but say that the current code is
>for inactive stations. Use the shift to signify an active station. Then
>use the time-out period to change to the inactive state.
This makes no difference in my argument. It isn't lower case that is the
problem, but the fact the the spec states that those characters can only be
N or S and E or W. Any other character there is garbage as far as an APRS
packet is defined for the last 12 years.
My example was meant to show that when faced with garbage, the results are
unpredictable. Some programs will assume an unexpected character in that
position is one of the valid characters, others will reject the packet
outright, still others might correctly parse it.
If anything is going to change there, lower case is better, because it
MIGHT not break some programs. It will CERTAINLY break others, so if a
change is to be made there, it should be something the APRS Working Group
considers carefully, and certainly not used on the air until the change has
been announced, and adequate time given for program authors to update their
programs and for users to deploy the new versions...
Personally, I am against this, but I don't feel strongly enough to mount an
argument on the proposal itself. My position is this is not the minor
change Bob sells it as, and it really needs to be considered carefully...
Steve K4HG
-+--------------------------------------------------------------------
Subject: Using A/D to sense stop/stop of vehicle (was: PCsat Endangered)
From: Jeff King <je...@aerodata.net>
Date: Sun, 18 Jan 2004 17:11:25 -0500
X-Message-Number: 23
On Sun, 18 Jan 2004 12:32:39 -0800, Derek Koonce wrote:
>If it is in the car, just find a voltage that will come on when the
>ignition is turned on and use this as a signal. Why bother
>monitoring the battery voltage since a no-load battery can be above
>12V. Derek KE6JTP
Because you don't have to find the wire, i.e. two wires for power instead
of three. The idea here is there is a voltage difference between when the
alternator is rotating, and when it is not rotating. Your putting the
difference to a secondary use. Since Scott wanted to monitor battery
voltage anyways, this is "free".
But if I was making this into a product, I'd still put a IGN input on it
for the few cases that can't take advantage of this, but I imagine most
folks would be happy not to have to run that third wire for ignition input.
You'd also need to put a little software filtering in it also, and only
turn off the unit if the GPS speed was at 0. Nice thing about this
circuit/algorithm is it is "cigerette lighter' friendly.
Another thing you could do, if the unit is "off" is look for a voltage DIP,
and that would indicate the user is trying to start the vehicle. That way,
even if you had a bad alternator, the unit would come on, and go off, when
the vehicle is stopped.
Software/firmware is such a wonderful thing....
-+--------------------------------------------------------------------
=== End m_006532.mes ===
*73! С уважением: Igor*
*Nizhny Novgorod (RA3TW Amateur Radio Station)*