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Re: Hobbyist battery SMPS circuit
by Neil Cherry-3
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Vasile Surducan wrote:
> On 5/8/08, Neil Cherry <ncherry@...> wrote:
>
>> Also are there relays that can be activated by 3V?
>
> Low voltage logic families (0.9V, 1V, 1.2V, 1.8V, 2.5V, 3.3V) have
> been invented to minimise power dissipation. If you are using a
> microcontroller supplied at one of these voltages and think to drive a
> 3V relay, I think something is wrong with your decision. As long you
> didn't say wahy you need a 3V relay I can only guess.
> Example of wrong decision: relay battery activated.
I'm not sure I follow, using the battery power supply is not a
choice, it's a requirement. It may be one to doom the project
but that is okay also. This project is 'driven' by my friend
and his needs for this odd-ball circuit. I initially wasn't
going to discuss what we're building but I will as it just
makes the discussion easier. My friend saw an article on a
'Cheese box' (a circuit that connects two POTS lines together)
and wants one for where he works. He wants to use it to connect
to old analog PBXs together POTS). I've looked at the circuit
and I don't like it. I'll be adding niceties to handle the
600V hot boxes they use to fix the copper and a few other
things. The reason behind the device is that they can't get
funding to properly connect the two circuits. This device
will make my friends life easier at work. This will not be
connect to the PSTN and it's not illegal. The use of batteries
and low power is to see if we can do it. I suspect we'll
eventually have to use local power (may be DC but not -48v)
but I'd like to see 'how low can we go'. I'll be using
an MSP430-2012 (I have 12) though I can use any number of
devices I already have.
Also if you're getting the impression that I don't know what
I'm doing you are correct, but I'm about to learn. The last
time I used a uC (micro-controller) to drive a relay I
needed a transistor and a diode external to the relay and I
had an AC-DC linear power source (plenty of power). This
is more of a challenge from my friend to see if it can be
done. He does to me a lot and he knows I won't turn it down
even if I think it will fail. Half the fun is in the learning.
The relay in question will drive another set of relays that will
get their power from the energized circuit (turning it off is a
question for later at this point ;-). The only decision made so
far is that a pin on the uC will drive the relay which will
energize the other relays. After n amount of time the relay in
question will be turned off as it's not needed to hold the circuit.
The reasoning behind the 3v relay is that the CPU can be run from
1.1v - 3.3v. I'd prefer not have to build two SMPS circuits for
different voltages. I'm know I can make the whole thing work off
AC.
--
Linux Home Automation Neil Cherry ncherry@...
http://www.linuxha.com/ Main site
http://linuxha.blogspot.com/ My HA Blog
Author of: Linux Smart Homes For Dummies
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
> On 5/8/08, Neil Cherry <ncherry@...> wrote:
>
>> Also are there relays that can be activated by 3V?
>
> Low voltage logic families (0.9V, 1V, 1.2V, 1.8V, 2.5V, 3.3V) have
> been invented to minimise power dissipation. If you are using a
> microcontroller supplied at one of these voltages and think to drive a
> 3V relay, I think something is wrong with your decision. As long you
> didn't say wahy you need a 3V relay I can only guess.
> Example of wrong decision: relay battery activated.
I'm not sure I follow, using the battery power supply is not a
choice, it's a requirement. It may be one to doom the project
but that is okay also. This project is 'driven' by my friend
and his needs for this odd-ball circuit. I initially wasn't
going to discuss what we're building but I will as it just
makes the discussion easier. My friend saw an article on a
'Cheese box' (a circuit that connects two POTS lines together)
and wants one for where he works. He wants to use it to connect
to old analog PBXs together POTS). I've looked at the circuit
and I don't like it. I'll be adding niceties to handle the
600V hot boxes they use to fix the copper and a few other
things. The reason behind the device is that they can't get
funding to properly connect the two circuits. This device
will make my friends life easier at work. This will not be
connect to the PSTN and it's not illegal. The use of batteries
and low power is to see if we can do it. I suspect we'll
eventually have to use local power (may be DC but not -48v)
but I'd like to see 'how low can we go'. I'll be using
an MSP430-2012 (I have 12) though I can use any number of
devices I already have.
Also if you're getting the impression that I don't know what
I'm doing you are correct, but I'm about to learn. The last
time I used a uC (micro-controller) to drive a relay I
needed a transistor and a diode external to the relay and I
had an AC-DC linear power source (plenty of power). This
is more of a challenge from my friend to see if it can be
done. He does to me a lot and he knows I won't turn it down
even if I think it will fail. Half the fun is in the learning.
The relay in question will drive another set of relays that will
get their power from the energized circuit (turning it off is a
question for later at this point ;-). The only decision made so
far is that a pin on the uC will drive the relay which will
energize the other relays. After n amount of time the relay in
question will be turned off as it's not needed to hold the circuit.
The reasoning behind the 3v relay is that the CPU can be run from
1.1v - 3.3v. I'd prefer not have to build two SMPS circuits for
different voltages. I'm know I can make the whole thing work off
AC.
--
Linux Home Automation Neil Cherry ncherry@...
http://www.linuxha.com/ Main site
http://linuxha.blogspot.com/ My HA Blog
Author of: Linux Smart Homes For Dummies
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
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