Alt-BEAM Archive
Message #06007
To: "'beam@sgiblab.sgi.com'" beam@sgiblab.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Thu, 9 Sep 1999 13:24:11 -0700
Subject: [alt-beam] Re: PS HEAD V2
Hiya Darrell,
This PS circuit is evolving and improving as we speak. The main advantage is
control of the high frequency noise that occurs in V1 and which can affect
timing. This is a big problem with 74AC240s, less with 74HC240s and none
with 74C240s (if you can find them).
Attached is my favorite variation of the PS circuit using a 74AC04. This is
the new improved PS_HEAD3. The circuit can be fine tuned by adjusting the
value of the 5M pot in series with the 5.1M resistor between the HLO and the
Nv/Nu stage which controls the behaviour when the sensors are balanced. With
10.1M total there is a narrow "dead band" when the sensors balanced where
power is shutdown. There is also little or no linear adjustment of the PWM :
it either full left, full right or stop. In very dark conditions the head
goes to sleep drawing less than 1 ma of current at 5V . With the pot
adjusted for 7.5M total resistance, the deadband (head stopped), is very
narrow and very small imbalances will start the head turning pulsing slowly
left or right. With a large imbalance, the head turns full speed left or
right. The behaviour is very "lively and sensitive" with rotation speed
proportional to the light difference. In very dark conditions the head will
pulse very slowly in one direction seeking a light source. With the total
resistance adjusted around 5M speed the head starts to look rather
nervous, shaking and hunting when locked on to a light source. In the dark
the head turns full speed in the direction of the sensor imbalance
(determined by the imperfect match of sensors). The behaviour is also
sensitive to the Vcc voltage and the description applies to a Vcc of +5V. At
lower voltage, different settings will be required. This circuit is very
compact and easy to freeform. I used small 2x2 Radio Shack perf boards to
keep the assembly neat.
enjoy
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411
<>
> -----Original Message-----
> From: Darrell Johnson [SMTP:beamtastic@yahoo.com]
> Sent: Wednesday, September 08, 1999 9:21 PM
> To: beam@sgiblab.sgi.com
> Subject: Re: PS HEAD V2
>
> Wilf, is there a big difference in the performance between v1 and v2 of
> the PSH? I was just curious, since I built the v1 PSH and it performs
> very well for me..
> I'm sure this will be of interest to others, so I'm posting it to the
> list..
> thanks..
>
> Darrell
> (I'm planning on breadboarding PSHv2 as soon as I get back home next
> week...)
>
> --- Wilf Rigter wrote:
> <>
>
> ===
> _______________________________
> BICOREEOS..They're BEAMtastic!!
> http://home.pacbell.net/wundoba
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Attachment: PSHEAD3.gif
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