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Re: [SIGMusic] circuit



I don't get it. Don't the transistors make sure that the solenoids are
not always being powered? They allow current to flow from the collector
to the emitter or not depending on whether current is flowing to the
base. The base is wired to the output pins of the PIC; we set the output
pins either high or low to turn the solenoid on and off.

A flip-flop would be necessary if we couldn't have our output pins be
continuously on or off.

... come to think of it, we could use a 6->64 demultiplexer in front of
48 D flip-flops to allow us to address 48 transistors with only 7 output
pins. Every time a note is played, we would send a pulse out to every
flip-flop to turn it on or off.

This would let us get by with only one PIC (and a smaller one at that),
but there's a little more incidental circuitry involved. We should keep
it in mind, though, in case we end up having a problem with the way
we're doing it now.

and because I'm bored, here's a transistor...
 
 (from 5V output pin on PIC)
       base
      /-----\
     /   |   \
     | __|__  |
     \/     \/
      \-----/
collector    emitter
(from +24V)    (to solenoid)

On Sun, 2007-02-25 at 12:04 -0600, Stephanie Bayani wrote:
> the pic is a switch.  however, we have 1 power supply.  so we could
> power the solenoids directly, however, we would need a "switch", to
> make sure teh solenoids are not getting power constantly.  switches
> actually are expensive, however if a 24V flipflop existed, we could
> probably do it.  yeah, but 24V, yeah right.  the suggestion i got was
> to make the flipflops from the transisters.  that sounds even more
> iffy.  haha.  
> 
> there's got to be a way to do this.   however, that is not the circuit
> we were at by the end of the day.  
> 
> i'll draw both circuits & email them by tonite.  (one powered by the
> chip, and one the chip is only a swtich) 
> 
> steph
> 
> 
> 
> On 2/25/07, Jacob Lee <jelee2@xxxxxxxx> wrote:
>         On Sat, 2007-02-24 at 22:35 -0600, Stephanie Bayani wrote:
>         > i talked to a friend a little about the circuit we're
>         making.
>         >
>         > he basically said it would work.  however...we run the risk
>         of killing
>         > lots of circuit boards.  as well as the solenoids.  using a
>         pic to
>         > provide power is basically bad design.  but whatever, we
>         don't care.
>         > and his question was can you even find a transister that
>         will pull 
>         > up..what is it?  15mA - 50mA (or 75mA)?  or .83V - 24V?  i
>         am assuming
>         > we did find transisters.
>         >
>         
>         I thought the point of the transistors was that so we *aren't*
>         using the
>         PIC to provide power. We just use the pic to switch on and off
>         the 
>         transistors -- which I suspect would be pretty normal. The
>         ones that I
>         speced are the 2N3904, which support up to 40V/200mA and are
>         only $0.10
>         each (not to mention the ACM has a ton that we may or may not
>         be able to 
>         use).
>         
>         (We also need a few 2N2222A transistors, which are 40V/800mA,
>         for the
>         500mA solenoid valves... see below).
>         
>         http://www.kpsec.freeuk.com/trancirc.htm#chip talks about
>         choosing a
>         transistor. I'm not sure if we're ok by those standards or not
>         (I'm not
>         sure I understand the bits about current gain). Also, the
>         section above
>         it talks about needing a diode across the solenoid to protect
>         against 
>         voltage spikes. Those should be another cheap part that we can
>         get from
>         the ECE store (if ACM doesn't have 50 of them lying around).
>         
>         > i'm not entirely sure that we need the volt regulator,
>         unless we can't 
>         > control the voltage output.  it's only amps, right that we
>         can
>         > control.
>         >
>         
>         We need something to get 5V for the PIC from the 24V supply.
>         The voltage
>         regulator is like $1.50 and gives us 5V out for up to 30-ish
>         volts in. 
>         It has a zener diode or something in it to make us less likely
>         to fry
>         the chip.
>         
>         > he suggested using flip flops (D).  and something about
>         Darlington.
>         > whatever.
>         >
>         
>         > if i'm reading the specs correctly, the amps / volts out of
>         a single 
>         > pin changes depending on what pins are in use / or on.  that
>         sucks ass
>         > and i hope i read that wrong.
>         >
>         
>         Yipes. Where is that in the spec? That could be scuzzy, but if
>         I'm
>         reading the data sheet for these transistors correctly 
>         ( http://www.fairchildsemi.com/ds/2N/2N3904.pdf ), anywhere
>         from 1-5V
>         will turn them on.
>         
>         > eh, i left my backpack in my friend's car, and i don't know
>         when i'll 
>         > get it back because of the weather.  i'm just gonna write
>         down
>         > everything that we supposedly know.
>         >
>         > 5 I/O ports
>         > PortA : 6 input/output
>         > PortB : 8 input/output
>         > PortC : 8 input/output 
>         > PortD : 8 input/output
>         > PortE : 3 input/output
>         >
>         > Port A+B+E has a sink/source max of 200mA.
>         > Port C+D has a sink/source max of 200mA.
>         >
>         > each indidvidual pin has a sink/source max of 25mA. 
>         >
>         
>         As long as the transistors draw less than 25mA each, we're ok.
>         I don't
>         know how to find this out. (Wit might know).
>         
>         > the pic needs 5V (high).  actually this can go to 5.5V,
>         but..that
>         > would probably be risky as far as frying stuff goes.
>         >
>         > each pic will handle 2 instruments.
>         >
>         > that's 11 solenoids and 1 solenoid valve controlled by 1
>         pic.
>         >
>         > all 12 outputs will each have a single transister. 
>         >
>         > the solenoids need 24V / 50mA.
>         > the solenoid valves needs 24V/ 75mA
>         >
>         
>         Two of the solenoid valves draw 75mA, and two draw 500mA. It's
>         what we
>         could find on ebay. :-p
>         
>         > the TRISx register will denote whether a i/o pin is input or
>         output. 
>         > this is done with the pic assembly and is part of the setup
>         for the
>         > ports.  (TRISA for porta, and TRISB for portb...)
>         >
>         > i'll draw a circuit diagram later.  it might be paper
>         format, since i 
>         > suck at drawing on the computer.
>         >
>         > i'll look at teh stupid diagrams, however, the graphs don't
>         mean a
>         > whole lot to me.  i have a vague memory of "sharing" graph
>         diagrams
>         > with former classmates.
>         >
>         > steph
>         >
>         
>         --
>         Jacob Lee <jelee2@xxxxxxxx>
>         
>         
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