Chip with simple program for Toy

[Andrew Holme]

Danny T wrote:

Andrew Holme wrote:

No, that won't work. The power supply would short-circuit through
a
diode and a MOSFET. You have to use the H-bridge configuration:
http://www.google.co.uk/search?q=motor+mosfet+%22h-bridge%22

Thanks Andy. Found this:

http://www.dprg.org/tutorials/1998-04a/hb6.png

Yep, that's an H-bridge; using bipolar transistors.

So do I just need some PNP mosfets the same as the NPN ones I already

have?

You need P-channel MOSFETs. The terms NPN and PNP apply to bipolar
transistors. MOSFETs are either: N-channel, or P-channel.

Is it possibly to drive two MOSFETs (the PNP from one side, and
NPN from the other) from the same IC pin?

Only via an inverter: the high-side MOSFETs turn-on when the gate is
low.

The high-side transistors are tricky to drive when the motor runs off a
different voltage to the controller. You might be better off looking
for a monolithic high-side driver like Anthony suggested.

 

[Anthony Fremont]

"Danny T" <danny@nospam.oops> wrote in message
news:41e5321b$0$44975$ed2e19e4@ptn-nntp-reader04.plus.net...

Anthony Fremont wrote:

You can use the mosfets you've already obtained for the low side
switching, but you will need something different for the high side
switch. You could use some standard p-channel mosfets, but
switching
them on can be a pain. I really like these things, they are quite
neat:

http://www.rapidelectronics.co.uk/rkmain.asp?PAGEID=80010&CTL_CAT_CODE=30412&STK_PROD_CODE=M34955&XPAGENO=1
They are often called smart power switches because they contain more
than just a p-channel mosfet, they are usually short-circuit
protected
and have the ability to tell you if the circuit is open. They also
contain all the necessary circuitry to take a logic level input and
apply the appropriate gate drive to the internal transistor. I
think
they were primarily developed for the automotive industry, but would
work well in your application.

That all sounds fantastic, but while I'm testing and potentially
destroying things, they're probably a bit OTT (and expensive),
especially in comparison to the low-side ones I've got! (about 50p
each!)

Well, like I said, the nice thing about the smart switches is that they
are often short circuit and reverse polarity protected. I paid US $1.60
ea for some 9A 36V (VN820) switches. Keep in mind that most things
designed for automotive use are usually pretty durable. This is what I
have, in the pentawatt case (5-pin TO-220):
http://www.st.com/stonline/books/pdf/docs/7370.pdf
I really don't like the case (pin layout), it's workable.

 

[Terry Pinnell]

Danny T <danny@nospam.oops> wrote:

I've got little motors that change direction if you reverse the
polarity. What's the best way to achieve this from a PIC? I was thinking
something like this:
This thread

Newsgroups: sci.electronics.design
Subject: Motor Control Circuit Problem
Date: 28 Oct 2004 15:48:41 -0700
news:1099003721.067016.22050@c13g2000cwb.googlegroups.com
may be of interest

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[Danny T]

Anthony Fremont wrote:

But the real show-stopper, I think, would be the fact that
the whole "radio" is inside the mouth, surrounded by
conductive tissue with no antenna protruding... a pretty
good Faraday cage, I reckon. (Or maybe the radio
only works when you stick out your toungue...!)

And it just so happens that your teeth are "tuned" perfectly to a
local
station?

Well that's the really neat thing about AM demodulation, you don't have
to have anything tuned. You only need a simple rectifier.

I don't understand - my stereo can tune into different AM stations! :-\

--
Danny

 

[Anthony Fremont]

"Danny T" <danny@nospam.oops> wrote in message
news:41e548e0$0$73812$ed2619ec@ptn-nntp-reader03.plus.net...

Anthony Fremont wrote:

But the real show-stopper, I think, would be the fact that
the whole "radio" is inside the mouth, surrounded by
conductive tissue with no antenna protruding... a pretty
good Faraday cage, I reckon. (Or maybe the radio
only works when you stick out your toungue...!)

And it just so happens that your teeth are "tuned" perfectly to a
local
station?

Well that's the really neat thing about AM demodulation, you don't
have
to have anything tuned. You only need a simple rectifier.

I don't understand - my stereo can tune into different AM stations!
:-\

That's because it is employing *selectivity*, in the front-end and in
the IF section(s). The nature of AM broadcast signals make them very
easy to convert directly to audio frequencies. An antenna, a diode, and
a ground connection are all that is needed to demodulate a strong AM
signal. A set of high impedance headphones across the diode will allow
you to listen. Just like this:
http://science.howstuffworks.com/radio9.htm
It's actually a bit more complex in that what really (as in the real
world) constitutes an antenna and a ground can get kind of odd. ;-) If
you want to do more complex things (like actually chose a station), you
will need to use tuned circuits and active semiconductors to improve
selectivity, sensitivity, output volume etc...

 

[SioL]

"Danny T" <danny@nospam.oops> wrote in message news:41e548e0$0$73812$ed2619ec@ptn-nntp-reader03.plus.net...

Anthony Fremont wrote:

But the real show-stopper, I think, would be the fact that
the whole "radio" is inside the mouth, surrounded by
conductive tissue with no antenna protruding... a pretty
good Faraday cage, I reckon. (Or maybe the radio
only works when you stick out your toungue...!)

And it just so happens that your teeth are "tuned" perfectly to a
local
station?

Well that's the really neat thing about AM demodulation, you don't have
to have anything tuned. You only need a simple rectifier.

I don't understand - my stereo can tune into different AM stations! :-\

Its quite simple, take 10-20m of wire and spread it around, if possible to a tree.
Make a simple detector with a shottky or germanium diode with smoothing cap,
attach sensitive headphones to the output of detector and you've got AM radio.

It will pick up strongest local station, no tuning needed.

SioL

 

[John Popelish]

Dominic-Luc Webb wrote:

2N3055 does this:

16.2 ___ ___ ___
| | | | | |
16V --- ---- ---- ---

Never drops to ground potential. It can in some cases go to roughly
12 times high frequency, as well.

Dominic

I can't think that your 2N3055 is good, unless you have reversed the
base and emitter pins or something similar. It has a lot more charge
storage than the smaller transistor, so it is harder to turn it on and
off quickly, but at this frequency, that should behave very similarly,
except for leakage and rise and fall time. What you describe is not
explained by the difference in the two types.

--
John Popelish

Thanks John!

I suspect it is bad, and I'll plan to try a new one. I do not think the
spec sheets, combined with the info I got with the transistor when I
bought it are very ambiguous, so wiring is certainly correct. The overall
circuit is correct since it works with all other transistors, taking into
account Ic and Ib, etc for each transistor.

Regarding the spec sheet you mentioned:
http://rocky.digikey.com/WebLib/ST%20Micro/Web%20Data/2N3055,%20MJ2955.pdf

I could not help noticing that here too, DC Current gain (hFE* in
Electrical Characteristics section) is specified as Vce = 4 Amps. Is
it is ever correct to state Vce in amps or typo? This is confusing.

Definitely a typo. Since Hfe is not an inherent property, but a
result of a combination of factors, a meaningful Hfe spec always
includes both a collector current (Ic) and a collector to emitter
voltage (Vce).

For the next level of complexity, I believe that the low beta of the
2N3055 means it has a narrow dynamic range (varying Ic with fixed base
voltage and resistor) in which it will operate normally.

By "normally" I assume you mean as a switch.

If I understand
these transistor specs and math correctly, I believe this also means that if
I have a varying load, as would be the case with a photomultiplier tube
pulling current from a transformer driven via this transistor, then a much
larger beta could be desirable (i.e., more dynamic range).

Higher beta implies that you need less drive current into the base to
produce a given collector current. But you can usually provide excess
base current to handle the high current case, without messing the low
current case up, too much. The usual 'cost' is longer turn off time.
Driving any switching transistor with a large voltage and large series
resistor approximates a current source, which aggravates the turn on
and turn off time problems. Slightly more complicated drive schemes
(adding a base to emitter resistor to drain the stored charge out
faster at turn off and paralleling the series resistor with a small
capacitor to drive the transitions harder) can result in significant
efficiency improvements.

I think a PMT can
draw anything from 1 nA to 1 mA. The counts per second in pulse counting
mode can go from a few hundred to 10's of millions.

Sounds about right.

--
John Popelish

 

[peterken]

"Danny T" <danny@nospam.oops> wrote in message
news:41e5282b$0$73821$ed2619ec@ptn-nntp-reader03.plus.net...

Andrew Holme wrote:

Would one of these per motor do?


http://www.rapidelectronics.co.uk/rkmain.asp?PAGEID=80010&CTL_CAT_CODE=&STK_PROD_CODE=M60258&XPAGENO=1

Any advantages to either way (using these, or doing something similar
to my first post)?

Yes, you could do it with a relay. You need a back e.m.f. protection
diode
across the relay coil and a MOSFET to drive it from the PIC. An
all-semiconductor solution might be more elegant (H-bridge) but a relay
is
simpler.

I've just been looking on rapid (www.rapidelec.co.uk) where I got my
N-channel MOSFETs, but they don't seem to have any similar P-Channel
ones. None rated at 1A of the same product, and some of the other
products are 80-100V, and/or don't say if they're NPN or PNP :-(

--
Danny

There IS another way, but it needs building a half-supply-voltage-regulator
(if it isn't available yet as a middle connection of a transformer)

something like this....

Vcc
O--+----+------------+-
\ | |
R/ |c s|
\ |/ +-||
+---| npn <-||
| |\e d+-||--- hi drive
| | |===| |
| +----| M |---+
| |e |===| |
| |/ d+-||
+---| pnp ->||
\ |\ +-||--- low drive
R/ |c s|
\ | |
O--+----+------------+---
GND

note the "half-supply" on the left, might be the middle-connection of the
supply transformer
(and yes, I disregarded snubber-diodes, I know, but it's the principle....)

 

[Danny T]

SioL wrote:

Its quite simple, take 10-20m of wire and spread it around, if possible to a tree.
Make a simple detector with a shottky or germanium diode with smoothing cap,
attach sensitive headphones to the output of detector and you've got AM radio.

It will pick up strongest local station, no tuning needed.

It's true about learning something new every day! I've learnt a lot more
from this group in the last few weeks though - think I'll stick around!!

--
Danny

 

[Andrew Holme]

Danny T wrote:

Andrew Holme wrote:

Is it possibly to drive two MOSFETs (the PNP from one side, and
NPN from the other) from the same IC pin?

Only via an inverter: the high-side MOSFETs turn-on when the gate is
low.

Then how about tunning the PNP and NPN from the same side on a single
pin? Would they change properly together, or could there be a period
where the P-channel has closed (on a low) before the N-channel has
opened (on the low)?

Yes, you can do that.
Yes, the logic transition needs to be fairly fast; but that shouldn't be a
problem.

There's an example circuit in the thread Terry P cited.

The high-side transistors are tricky to drive when the motor runs
off a different voltage to the controller. You might be better off
looking for a monolithic high-side driver like Anthony suggested.

I don't understand

For the lower (N) transistors, the PIC has no problem producing the OFF
voltage (zero).
For the upper (P) transistors, the OFF voltage = motor power supply.
Some sort of level conversion stage may be required in-between.
If you ran the motor from 3V, a P-channel logic-level drive MOSFET would
need 3-5 = -2V to turn-on. You would be better of making the H-bridge with
bipolar transistors for 3V motors.

I've been thinking about having seperate supplies for my motors and
pic. I'll use diodes while it's plugged into the wall, but when
running on batteries, I'll have a set for the motors, and a set for
the pic. Should I connect the grounds together, or keep everything
seperate? (surely I need to connect them since the MOSFETs drain and
gate both need source to be grounded for their circuits?

Yes, you must connect the grounds together to establish the common reference
level.

 

[Robert Monsen]

Danny T wrote:
<snip quest for a reversable motor>

Regarding motor reversal, you probably want to use an integrated IC that
is designed for this. One that I use is this one:

http://www.acroname.com/robotics/parts/R6-754410.html

(I probably wouldn't buy it there though. You could probably buy 4 at
arrow for the price of one here).

There are lots of advantages to this chip over the discrete solution you
are considering, including the ability to drive a higher voltage motor,
circuitry to prevent 'shoot through', which must means having the high
and low driver on one side turned on at the same time (which causes
spikes on the supply), etc. It takes 4 PIC pins to run 2 motors (or 6 if
you want to separately control the enables).

You need to buy some 'fast' diodes as well to protect the drivers from
reverse voltages. Look at the datasheet for more info.

The only real liability is the power limit.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[JeB]

On Fri, 07 Jan 2005 03:25:40 GMT, dewarg**NOSPAM**@nbnet.nb.ca (George
Dewar) wrote:

In article <zM_Cd.204764$Np3.8607734@ursa-nb00s0.nbnet.nb.ca>, dewarg**NOSPAM**@nbnet.nb.ca
says...

I would like to have somebody knowledgeable in electronics construct a device

Have a look at <www.geocaching.com>. The LED will mark a cache meant to be found at night probaly
in a wooded area. The light should be visible for 180 degrees at about 50 feet and run for a
reasonable length of time on battery power.

Thanks to those who have responded.

there's a chip (LM3909)that will flash an LED for a long time using a
single 1.5v cell. the 180 degree issue might mean using several of them
depending on the coverage of the LED you pick. There are inexpensive
ready made flashers for cyclists/hikers but they don't have the on at
dark/off at dawn option as far as i know.

 

[Danny T]

Andrew Holme wrote:
<snip>

These:

http://www.rapidelectronics.co.uk/rkmain.asp?PAGEID=80010&CTL_CAT_CODE=&STK_PROD_CODE=M34947&XPAGENO=1

(and others on Rapid) don't say if they're N-channel or P-channel. I've
checked a few datasheets with no avail too. They're called "power
MOSFETs", but I don't know if that means they're P or not... The item
number (VNP10N06) has both an N and P in! It also says "omnifet", if
that suggests either! :-\

The datasheet (if I'm reading it right) says a min of 3.2V will switch
it, but it says "Vdd = 16". My supply is only 4-5V - would this be a
problem?

 

[David Harmon]

None of the newsgroups in the sci.electronics.* hierarchy are intended
for buying and selling. An obvious giveaway is that none of them have
"forsale" or "marketplace" in their name.

See Mark Zenier's guide to the hierarchy, at
ftp://ftp.eskimo.com/u/m/mzenier/seguide9706.txt

When sci.electronics was split back in '95, an associated newsgroup
was created for buying and selling:
misc.industry.electronics.marketplace

http://pages.ebay.com/help/welcome/usenet-policy.html
Quote:
eBay users may not post on Usenet groups (Internet newsgroups) to
advertise eBay or an eBay listing that is inappropriate or violates the
Usenet board policy. If Usenet abuse is reported to eBay, we may among
other remedies remove the listing, issue a warning, or suspend the
user's eBay account.

 

[Bob Masta]

On Wed, 12 Jan 2005 11:08:51 +0000, Danny T <danny@nospam.oops> wrote:

Bob Masta wrote:

But the real show-stopper, I think, would be the fact that
the whole "radio" is inside the mouth, surrounded by
conductive tissue with no antenna protruding... a pretty
good Faraday cage, I reckon. (Or maybe the radio
only works when you stick out your toungue...!)

And it just so happens that your teeth are "tuned" perfectly to a local
station?

Well, it helps if your teeth look like the pushbuttons on an old
car radio... just bite down on the proper tooth! ;-)



Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

[Danny T]

Andrew Holme wrote:

The schematic in the PDF, with the source arrow pointing into the
MOSFET, indicates N-channel.

I see... Still, a lot of trouble to go to to find out!

This device looks a bit OTT for your application.

Where does it say "Vdd=16"? Do you mean "Vdd=15" in the "Test
Conditions" column? That's just the voltage they took the measurement
at. The MOSFET will switch any voltage up to the specified max.

Dunno, can't find 16 now... I don't think it was under test conditions,
but I may've been wrong. Thanks!

Got a postcard from the library today to say The Art of Electronics
arrived (I had to order it), so I'll start going through it later -
looks like a big read ;-)


--
Danny

 

[Danny T]

Andrew Holme wrote:

You would be better of making the H-bridge with
bipolar transistors for 3V motors.

Now you're confusing me!

Think I'll go read this book...

--
Danny

 

[Danny T]

Andrew Holme wrote:

There's an example circuit in the thread Terry P cited.

On this page:

http://www.cs.uiowa.edu/~jones/step/circuits.html

Figure 3.14 shows a couple of diodes, a couple of resistors and 4xBD679
darlington transistors. On Rapid, they're 81-0106, 25p+vat.

I assume X and Y could be connected to my PIC? Outputs are 4-5V from my
pic. Would the digram there work as is for me (it's around 4-5V motor),
or would I need to change anything? (How does is the voltage to the
motor controlled?)

I'm gonna go start reading The Art of Electronics, but I want to order
the bits I'll need asap, so I can start fiddling!

Ta,

--
Danny

 

[Danny T]

Anthony Fremont wrote:

I don't understand

Don't worry, it gets harder. ;-)

Excellent! Just what I was hoping you'd say ;P

High side switching is kind of a pain (go read a p-channel MOSFET
datasheet and pay close attention the voltage that is needed on the gate
with respect to the source voltage, also look at the horrid RDSon
values), that is why the monolithic power switch devices exist. They
also make it possible to apply the same +5V signal that you are applying
to the low-side MOSFET to switch them on, instead of needing a voltage
inversion.

That sounds too easy - what's the catch?

You can also use N-channel transistors on top, but then you have to come
up with a voltage higher than your motor supply to turn them on fully.
That's because the Vds is really small when the transistor is on, AND
(for the transistor to be fully on) the Vgs has to be at least 4V for a
logic level MOSFET. In order to get the gate at a high enough voltage,
you will have to apply 16V (if your motor supply is 12V) to the gate.
How ya gonna do that? ;-)

My motors are only around 4V, but I see what you mean. Why can't the
real world be software emulated - it's much easier to work with


--
Danny

 

[Robert Monsen]

Danny T wrote:

Robert Monsen wrote:

Regarding motor reversal, you probably want to use an integrated IC
that is designed for this. One that I use is this one:

http://www.acroname.com/robotics/parts/R6-754410.html

(I probably wouldn't buy it there though. You could probably buy 4 at
arrow for the price of one here).

There are lots of advantages to this chip over the discrete solution
you are considering, including the ability to drive a higher voltage
motor, circuitry to prevent 'shoot through', which must means having
the high and low driver on one side turned on at the same time (which
causes spikes on the supply), etc. It takes 4 PIC pins to run 2 motors
(or 6 if you want to separately control the enables).

You need to buy some 'fast' diodes as well to protect the drivers from
reverse voltages. Look at the datasheet for more info.

The only real liability is the power limit.


That looks less fun. I want to learn as much about electronics as I can,
so the more "diy" I do, the better
(it does mean I'll be anal about asking questions in here a lot though!)

That's fair.

However, I've found that it simplifies one's robot quite a bit, so it's
then possible to get on to the more interesting parts, which are the
sensors and software to guide it. It will handle two small DC motors. At
a couple of bucks, it's probably cheaper than 8 power transistors as well.

There are lots of tutorials you can look over on www.acroname.com, which
is a robotics site. There are also about 20 robotics newsgroups which
you might be interested in joining.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.