Alt-BEAM Archive

Message #02817



To: beam beam@corp.sgi.com, Chiu-Yuan Fang chiumanfu@home.com
From: Sean Rigter rigter@cafe.net
Date: Fri, 30 Apr 1999 10:02:31 -0700
Subject: [alt-beam] Hysteresis Solar Engine (HYSE)



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Hello all,

After a few false starts I'm back on track with a new tested SE design.
This was build to prove that the hysteresis of a supervisory chip can be
increased and used for SE latching. It was tested using a MC34164 (5V)
voltage supervisor since I have no 1381 to play with. It worked fine
with a range of input currents ma to 30 ma using a simulated 9V OCR
solar cell.

The design was breadboarded and tested with 3 different motors including
the relatively common Mac ejector motor. With the 0.047F cap shown and 5
mA supply current @ 5V, the Omron motor runs for about .5 sec every 5
sec and the output shaft turns about 90 degrees for each pulse (which,
incidentally, is exactly what is needed for a walker application but
that's another design)

The way that the hysteresis is increased is worth mentioning. In this
circuit with V+ = 5.2V, the supervisor is still operating below the
threshold (!) This happens because the 34164 output is low and the 50 uA
current flowing through the 100K resistor also flows through the 10K
resistor raising the trigger threshold by 500mV. When the supervisor
trips at about 5.3V, the output changes from 500mV to 5.3V and the
current through the 100K and 10K resistors drops to zero while the motor
current "snaps" on. When the voltage across the 10K resistor drops to
zero, this also drops the lower threshold voltage by about 500mV and
provides the required. hysteresis.

When the voltage drops down to about 4.8V, the supervisor output turns
back on and the process starts again. Since the supervisor output
voltage rises to about 500mV before the threshold is reached, the FETs
used must have a Vgs (@0.1mA) > 1.0V or else the circuit will not
work!

I have not yet build a complete working "photopopper" type application
with this circuit, so you take your chances. The design should be
scalable to other chips and voltages as long as the supervisor chip is
the non inverting active low/open collector type and the Vgs of the FETs
is higher than the Vhys at the lowest supply current of interest.

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2818 Fri, 30 Apr 1999 11:17:33 -0700 [alt-beam] Re: Smiley Steven Bolt Sean Rigter Very nice Steven,

a remarkable simple design! It's voltage controlled pulse frequency
modulation similar to the PWM idea. Very interesting to see this circuit
evolving. I guess the higher order logic gates of your earlier designs
were always considered too digital by some but diode logic used here is
ok (Hmmm? I wonder if that isn't devolution?)

I wonder if using 3 or 4 Si diodes in series with the 390K could
replace the transistor/LED? You could adjust 390K resistor value to
adjust the diode turn-on curve to give good voltage sensitivity. Of
course the capacitor and other resistors would need adjustment as well
to maintain the right motor pulse width and low voltage characteristics.

regards

wilf

Steven Bolt wrote:
>
> While waiting for the Suneater_V PCBs to arrive, I had time to
> finish an older project. Meet Smiley.
>
> His behaviour is based on three rules:
>
> 1. If no feeler switches are closed, the motors will obey the `eyes'.
> Smiley moves towards the best light, while trying to avoid shadow
> patches.
> 2. If one of the feelers touches an obstacle, Smiley "follows the wall" in
> the direction of the better light. Both this and the first behaviour
> are illustrated here.
> 3. With both feeler switches closed, the robot will push against one of
> them, trying to get free.
>
> My other solar-powered `bots show exactly the same behaviour. But
> Smiley is the first to manage with just one 74HC14 and one transistor
> as `brain'. Inspiration was provided by Wilf's talk of pulse-width
> modulation, two months ago. Pictures, schematic, PCB layout and all
> other details on:
>
> http://www.xs4all.nl/~sbolt/e-smiley.html
>
> Enjoy,
>
> Steve
>
> ----------------------------------------------------------------------
> # sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
> ----------------------------------------------------------------------

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