AVR-Chat

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
> > 
> > 
> > 
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> > 
> >  
> > 
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> > 
> > 
> 
> 
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