I would like to switch between two voltages, -12 and +12, this is no problem, as I will use two transistor circuits, but my question was, I get the voltage for the picaxe (5V) out of my PSU and I would also be getting the 12volts out of the same PSU, can I use a mutual ground in this circuit?
transitor interfacing circuit
- Thread starter Scuzzy47
- Start date
Michael 2727
Senior Member
You will need to run the picaxe from the
0 Zero Volt and +12Volt rails.
e.g.
<code><pre><font size=2 face='Courier'>
Plus +12V------ Here.
Zero ---------- Here.
Minus -12V----- </font></pre></code>
That is if you have a true split rail supply.
The tricky part will be switching the transistor
on the Zero 0V and -12V side.
Edited by - Michael 2727 on 12/06/2006 12:20:20
0 Zero Volt and +12Volt rails.
e.g.
<code><pre><font size=2 face='Courier'>
Plus +12V------ Here.
Zero ---------- Here.
Minus -12V----- </font></pre></code>
That is if you have a true split rail supply.
The tricky part will be switching the transistor
on the Zero 0V and -12V side.
Edited by - Michael 2727 on 12/06/2006 12:20:20
It is <i>essential </i> that all voltages used in your circuit have a common reference-point, i.e. meaning that the 0V points for all voltage rails <i>should </i> be tied together.
BTW: You used the term ‘ground’ in your post, (and it’s very common to refer to the 0V point as ground too), but in fact they can be two different things.
Sometimes DC electrical circuits will have their 0V point isolated from ground, or just have one connection to ground at a single location to prevent a troublesome condition known as ‘ground loops’ (also known as ‘earth loops’
.
Note also that if you are using a computer PSU for your voltage rails, BEWARE! If the PSU is not sufficiently loaded (i.e. only running your Picaxe), then the voltage will almost certainly be too high and will damage your chip. This is because computer PSU’s are designed to provide currents significantly greater than the comparatively microscopic current that a Picaxe requires.
PS: Just as I post this, I’ve noticed that you have received some other replies also.
So I hope you find this information of some use.
Cheers
BTW: You used the term ‘ground’ in your post, (and it’s very common to refer to the 0V point as ground too), but in fact they can be two different things.
Sometimes DC electrical circuits will have their 0V point isolated from ground, or just have one connection to ground at a single location to prevent a troublesome condition known as ‘ground loops’ (also known as ‘earth loops’
.Note also that if you are using a computer PSU for your voltage rails, BEWARE! If the PSU is not sufficiently loaded (i.e. only running your Picaxe), then the voltage will almost certainly be too high and will damage your chip. This is because computer PSU’s are designed to provide currents significantly greater than the comparatively microscopic current that a Picaxe requires.
PS: Just as I post this, I’ve noticed that you have received some other replies also.
So I hope you find this information of some use.
Cheers
hippy
Ex-Staff (retired)
This will work, but take care that the switching circuit does not short +12V to -12V ...<code><pre><font size=2 face='Courier'>.----------. .--------.
| +12V |-------------------------------->| SWITCH |---.---> +/-12V
| | `---.----' |
| | .--------. | |
| +5V |--------->| |-----------------' |
| | | PICAXE | |
| PSU | .--->| |-----------------. |
| | | `--------' | |
| | | | |
| 0V |-----^-------------------------------|--------|---> 0V
| | | |
| | .---^----. |
| -12V |-------------------------------->| SWITCH |---'
`----------' `--------' </font></pre></code> If you meant something else, you'll have to explain what you want in more detail.
| +12V |-------------------------------->| SWITCH |---.---> +/-12V
| | `---.----' |
| | .--------. | |
| +5V |--------->| |-----------------' |
| | | PICAXE | |
| PSU | .--->| |-----------------. |
| | | `--------' | |
| | | | |
| 0V |-----^-------------------------------|--------|---> 0V
| | | |
| | .---^----. |
| -12V |-------------------------------->| SWITCH |---'
`----------' `--------' </font></pre></code> If you meant something else, you'll have to explain what you want in more detail.
If you use Hippy's approach, it might be wise to use logic gates to drive your gates so that it is not possible to short your output by turning on both transistors at the same time. If your 12V supply is of any reasonable size (current wise), it is a very real possibility that the output stage could fry, or worse, catch fire! If the output can remain at either +12V or -12V (ie. one or the other but not off - 0V), then you should also be able to save one PICAXE I/O.
<b><i>ylp88 </b> </i>
<b><i>ylp88 </b> </i>
Thx hippy that's exactly what I needed, the only problem I have is that both 12 volts will be on all the time, so indeed, I'll have to work this out in my program, but that's manageble, I use this for a little motor that turns open or closes a watersupply, so when it gets to hot, it closes a bit more, when it gets to cold it opens the hot water... So if I can do it like Hippy sais it should work...
Thx for the help guys
Thx for the help guys
Michael 2727
Senior Member
What voltage is your motor.
If it is 12V you could forget the -12V side
and just run a H-bridge.
Or if 24V forget the 0 Zero rail and just
use the -12 as 0 Neg and the +12 as +24V with a
H-bridge and run the regulator across
the 24V although it will run fairly hot so a
good heatsink will be needed.
You could even run 2 regulators a 12V then into
a 5V as a pre-regulator to split the heat dissipation
up a bit.
And as Whizzer mentioned most switchmode
supplies e.g. computer PSU require a minimum load
at all times to help with voltage feedback
and regulation
so if the Picaxe will be the only thing drawing
current for much of the time you may like
to include
a 10W or 20W automotive type globe as a power
indicator to waste/use up a little current
which should keep the PSU happy.
Edited by - Michael 2727 on 12/06/2006 13:46:31
If it is 12V you could forget the -12V side
and just run a H-bridge.
Or if 24V forget the 0 Zero rail and just
use the -12 as 0 Neg and the +12 as +24V with a
H-bridge and run the regulator across
the 24V although it will run fairly hot so a
good heatsink will be needed.
You could even run 2 regulators a 12V then into
a 5V as a pre-regulator to split the heat dissipation
up a bit.
And as Whizzer mentioned most switchmode
supplies e.g. computer PSU require a minimum load
at all times to help with voltage feedback
and regulation
so if the Picaxe will be the only thing drawing
current for much of the time you may like
to include
a 10W or 20W automotive type globe as a power
indicator to waste/use up a little current
which should keep the PSU happy.
Edited by - Michael 2727 on 12/06/2006 13:46:31
BeanieBots
Moderator
If all you want to do is to run a motor in either direction, then why not simply use a two pole relay to do the reversing action and a single transistor for on/off. Such an arrangement is inherently safe (not possible to short power rails even with dodgey code) and far simpler/cheaper than an H-Bridge.