AVR-Chat

Hi

I am currently driving an AVR (mega 8) input from a SFH618A 
optoisolator being driven from the output of a radio control 
receiver. The input LED is driven from the R/C receiver via a 330R 
series resistor and the output transistors emmitter is taken to 
ground with a 3K3 resistor. The transistor collector is taken to +5V 
and to AVR is driven directly from the transistor emmitter pin. The 
LED is connected to ground on the R/C receiver. This works fine.

The problem is that I cannot find any other optoisolator that will 
work in this circuit and cannot find any new resistor values to work 
with the other optoisolators I have, (e.g SFH615, TLP504). The 
SFH618 is relatively expensive you see.

Can anyone recommend a good way of choosing resistor values or point 
me to a good "how to use optoisolator" type article please?

Mark

At 09:28 PM 30/11/03 -0000, you wrote:
>Hi
>
>I am currently driving an AVR (mega 8) input from a SFH618A 
>optoisolator being driven from the output of a radio control 
>receiver. The input LED is driven from the R/C receiver via a 330R 
>series resistor and the output transistors emmitter is taken to 
>ground with a 3K3 resistor. The transistor collector is taken to +5V 
>and to AVR is driven directly from the transistor emmitter pin. The 
>LED is connected to ground on the R/C receiver. This works fine.

Usually you would ground the emitter and use a pullup resistor
at the collector which feeds the input pin. This would give you
an inverted signal but that would not matter, it would just be
negative active. I would say that 100% of optos would work
this way.


Regards

John Samperi

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                        Ampertronics Pty. Ltd.
  11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
         Tel. (02) 9674-6495       Fax (02) 9674-8745
               Email: samperi@ampertronics.com.au
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* Electronic Design   * Technical Services   * Contract Assembly
******************************************************

Hi Mark,

I don't know these optos but, as a general rule, there are two things 
to watch out for. Current Trandfer Ratio (CTR) and speed. CTR is a 
bit like bipolar transistor beta - it is the ratio of output 
(collector) current to input (LED) current and is commonly as low as 
20% (0.2). You mention a 330R input resistor but not the voltage of 
the receiver output. Do you have an oscilloscope to view the receiver 
output?

There are a few factors that can influence speed. A trap is to use a 
darlington output - they are very slow compared to single transistor 
outputs.

Why are you isolating the input?

I hope that helps.

Regards,
Les.

On 30 Nov 2003 at 21:28, Mark Pepper wrote:

> Hi
> 
> I am currently driving an AVR (mega 8) input from a SFH618A 
> optoisolator being driven from the output of a radio control 
> receiver. The input LED is driven from the R/C receiver via a 330R 
> series resistor and the output transistors emmitter is taken to 
> ground with a 3K3 resistor. The transistor collector is taken to +5V 
> and to AVR is driven directly from the transistor emmitter pin. The 
> LED is connected to ground on the R/C receiver. This works fine.
> 
> The problem is that I cannot find any other optoisolator that will 
> work in this circuit and cannot find any new resistor values to work 
> with the other optoisolators I have, (e.g SFH615, TLP504). The 
> SFH618 is relatively expensive you see.
> 
> Can anyone recommend a good way of choosing resistor values or point 
> me to a good "how to use optoisolator" type article please?
> 
> Mark
> 
> 
> 
> To unsubscribe from this group, send an email to:
> AVR-Chat-unsubscribe@yahoogroups.com
> 
>  
> 
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ 
> 
> 


-------------------------------------------------------------
Les Grant. VK2KYJ.      Phone: 02 9896 7150 Fax: 02 9896 7153
Grantronics Pty Ltd     Int'l: +612 9896 7150, +612 9896 7153
PO Box 275                     mailto:info@grantronics.com.au
Wentworthville. NSW. 2145.      http://www.grantronics.com.au
Australia.                
Microcontroller Hardware and Software development:  Atmel AVR
8051 derivatives, 80C196 family, C, ASM, Digital and analogue 
-------------------------------------------------------------
Australian distributor for:
o Dunfield Development Systems low cost development tools
o ImageCraft AVR and Motorola Windows-hosted C compilers
o ELNEC Device Programmers (E)EPROMs, Flash, Micros, PLDs
o CAN-BUS Hardware and Software from LAWICEL
o Logical Systems Programming, Prototyping & Production Adaptors
-------------------------------------------------------------

On Sunday, November 30, 2003, at 05:09  PM, Les Grant wrote:

> Hi Mark,
>
> I don't know these optos but, as a general rule, there are two things
> to watch out for. Current Trandfer Ratio (CTR) and speed. CTR is a
> bit like bipolar transistor beta - it is the ratio of output
> (collector) current to input (LED) current and is commonly as low as
> 20% (0.2). You mention a 330R input resistor but not the voltage of
> the receiver output. Do you have an oscilloscope to view the receiver
> output?

The CTR can also change pretty drastically over temperature too...

Mike

You can use an electron microscope to read the memory according to
this PDF:

http://www.cl.cam.ac.uk/~mgk25/sc99-tamper-slides.pdf

If you know the precise location of the lock bit you might be able to
change its state by bombarding it with electrons.

If it were a simple job to read the memory of a "locked" AVR the lock
bit would be useless, right?

Have Fun!

--- In AVR-Chat@yahoogroups.com, "Emerson Santos"
<emersonsantosrj@u...> wrote:
> Hi people !!!
> 
> Anyone know a kind of "backdoor" in AVR to read a chip
> with a enabled LockBit ???
> 
> Could I read a PRG in Flash .. in this conditions ??? (lock bit =
ON)
> 
> Tanx'S ALL

Les

I am getting 5V ish pulses from the received. Pulses are between 
around 1 and 2ms long. I don't want to add any further circuitry 
like a following transistor.

Mark

--- In AVR-Chat@yahoogroups.com, "Les Grant" <lesgrant@g...> wrote:
> Hi Mark,
> 
> I don't know these optos but, as a general rule, there are two 
things 
> to watch out for. Current Trandfer Ratio (CTR) and speed. CTR is a 
> bit like bipolar transistor beta - it is the ratio of output 
> (collector) current to input (LED) current and is commonly as low 
as 
> 20% (0.2). You mention a 330R input resistor but not the voltage 
of 
> the receiver output. Do you have an oscilloscope to view the 
receiver 
> output?
> 
> There are a few factors that can influence speed. A trap is to use 
a 
> darlington output - they are very slow compared to single 
transistor 
> outputs.
> 
> Why are you isolating the input?
> 
> I hope that helps.
> 
> Regards,
> Les.
> 
> On 30 Nov 2003 at 21:28, Mark Pepper wrote:
> 
> > Hi
> > 
> > I am currently driving an AVR (mega 8) input from a SFH618A 
> > optoisolator being driven from the output of a radio control 
> > receiver. The input LED is driven from the R/C receiver via a 
330R 
> > series resistor and the output transistors emmitter is taken to 
> > ground with a 3K3 resistor. The transistor collector is taken to 
+5V 
> > and to AVR is driven directly from the transistor emmitter pin. 
The 
> > LED is connected to ground on the R/C receiver. This works fine.
> > 
> > The problem is that I cannot find any other optoisolator that 
will 
> > work in this circuit and cannot find any new resistor values to 
work 
> > with the other optoisolators I have, (e.g SFH615, TLP504). The 
> > SFH618 is relatively expensive you see.
> > 
> > Can anyone recommend a good way of choosing resistor values or 
point 
> > me to a good "how to use optoisolator" type article please?
> > 
> > Mark
> > 
> > 
> > 
> > To unsubscribe from this group, send an email to:
> > AVR-Chat-unsubscribe@yahoogroups.com
> > 
> >  
> > 
> > Your use of Yahoo! Groups is subject to 
http://docs.yahoo.com/info/terms/ 

> > 
> > 
> 
> 
> -------------------------------------------------------------
> Les Grant. VK2KYJ.      Phone: 02 9896 7150 Fax: 02 9896 7153
> Grantronics Pty Ltd     Int'l: +612 9896 7150, +612 9896 7153
> PO Box 275                     mailto:info@g...
> Wentworthville. NSW. 2145.      http://www.grantronics.com.au
> Australia.                
> Microcontroller Hardware and Software development:  Atmel AVR
> 8051 derivatives, 80C196 family, C, ASM, Digital and analogue 
> -------------------------------------------------------------
> Australian distributor for:
> o Dunfield Development Systems low cost development tools
> o ImageCraft AVR and Motorola Windows-hosted C compilers
> o ELNEC Device Programmers (E)EPROMs, Flash, Micros, PLDs
> o CAN-BUS Hardware and Software from LAWICEL
> o Logical Systems Programming, Prototyping & Production Adaptors
> -------------------------------------------------------------

Oh, MAN, that's a good link!

People are asking this question ALL THE TIME
about AVR's and PIC's -- and now here's
a definitive answer!  

So yes, this link gives you the technique.
First, you open the package.  In their case,
they used a smart-card, so they removed the 
CPU core from the card, then installed it in
an empty IC, using the aluminum wire/ultrasonic
connection machine.  

Our job is easier, maybe, as we don't have to 
do all of that -- just cut the top off the IC.
Easier said than done.

From there, you just probe the chip under a 
high-magnification workstation, restore the 
'lock' fuse, and you're good to go!

Unfortunately, it does take about $30,000 in
equipment (estimated) -- and some luck to not
destroy your chip when you open it.


--- In AVR-Chat@yahoogroups.com, "moriarty70" <moriarty70@y...> wrote:
> You can use an electron microscope to read the memory according to
> this PDF:
> 
> http://www.cl.cam.ac.uk/~mgk25/sc99-tamper-slides.pdf
> 
> If you know the precise location of the lock bit you might be able 
to
> change its state by bombarding it with electrons.
> 
> If it were a simple job to read the memory of a "locked" AVR the 
lock

> bit would be useless, right?
> 
> Have Fun!
> 
> --- In AVR-Chat@yahoogroups.com, "Emerson Santos"
> <emersonsantosrj@u...> wrote:
> > Hi people !!!
> > 
> > Anyone know a kind of "backdoor" in AVR to read a chip
> > with a enabled LockBit ???
> > 
> > Could I read a PRG in Flash .. in this conditions ??? (lock bit =
> ON)
> > 
> > Tanx'S ALL

Actually opening the chip is the easy part.  All you need is the
proper acid to eat the plastic bits but leave the chip.  

--- In AVR-Chat@yahoogroups.com, "Allan Lane" <allan.lane@h...> wrote:

> Oh, MAN, that's a good link!
> 
> People are asking this question ALL THE TIME
> about AVR's and PIC's -- and now here's
> a definitive answer!  
> 
> So yes, this link gives you the technique.
> First, you open the package.  In their case,
> they used a smart-card, so they removed the 
> CPU core from the card, then installed it in
> an empty IC, using the aluminum wire/ultrasonic
> connection machine.  
> 
> Our job is easier, maybe, as we don't have to 
> do all of that -- just cut the top off the IC.
> Easier said than done.
> 
> From there, you just probe the chip under a 
> high-magnification workstation, restore the 
> 'lock' fuse, and you're good to go!
> 
> Unfortunately, it does take about $30,000 in
> equipment (estimated) -- and some luck to not
> destroy your chip when you open it.
> 
> 
> --- In AVR-Chat@yahoogroups.com, "moriarty70" <moriarty70@y...> wrote:
> > You can use an electron microscope to read the memory according to
> > this PDF:
> > 
> > http://www.cl.cam.ac.uk/~mgk25/sc99-tamper-slides.pdf
> > 
> > If you know the precise location of the lock bit you might be able 
> to
> > change its state by bombarding it with electrons.
> > 
> > If it were a simple job to read the memory of a "locked" AVR the 
> lock
> > bit would be useless, right?
> > 
> > Have Fun!
> > 
> > --- In AVR-Chat@yahoogroups.com, "Emerson Santos"
> > <emersonsantosrj@u...> wrote:
> > > Hi people !!!
> > > 
> > > Anyone know a kind of "backdoor" in AVR to read a chip
> > > with a enabled LockBit ???
> > > 
> > > Could I read a PRG in Flash .. in this conditions ??? (lock bit =
> > ON)
> > > 
> > > Tanx'S ALL