Re: Tasks Accomplished Jan31

[Joyce Poon <poonj@ecf.utoronto.ca>]

On Tue, 1 Feb 2000, Tim Vanderhoek wrote:

> When you tried increasing the amplification factor of the circuit by
> using a larger resistor, which stage did you add it to?  If you added
> it to one of the first couple stages, that would explain why it did
> not work too well.  It needs to be added to the later stages.

I'm not THAT dumb.  I added it to the last stage. 

> I think you _may_ have better luck adding another stage to the amplifier if
> you put a small cap across the input to the extra stage and the ground
> line.

That kind of creates a low pass filter -- hence the circuit at that last
stage will have a band pass filter.  I think I tried that last time but
it didn't work.  One wonders whether adding that low pass filter will do
anything since there is, in theory, nothing oscillating at that freq range
other than our signal.

Actually -- band pass filters might not work very well at all --remember
when I changed the time scale on the scope, we saw that (at least I
saw that) the output was a squarish/sinusoidal wave modulating a bunch of
sinusoids oscillating at a much higher freq.  Using a bandpass filter may
filter out the quickly oscillating signal (ie the signal produeced by
unmodulated IR light itself) but not the modulated one.  This is rather
paradoxical.  I wonder if using band pass filters may in fact yield a zero
output.

Besides band pass filters make the sensors less flexible (ie it's harder
for us to change freq if we want to later).

Good thing that Tim doesn't care for band pass filters anymore, as stated
in his earlier email.

I drifted off topic.  I was going to boost sensor range by increasing the
voltage to the emitter.  The 555 timer can have a max Vcc of 18V.  I ran
it at 12V before with the power supply but the resistors got really hot
(this was not in lab).  Maybe the circuit won't draw as much current from
batteries.  In lab, the timer circuit only ran under 9V.  I plan to
increase it to 12 or even 15V.  Hopefully the signal will be stronger.

Joyce :)