Subject:New photovore circuit
Date:Mon, 1 Mar 1999 00:34:27 -0800
From:Wilf Rigter
To:"'Les Davis'" , Chiu-Yuan Fang ,
Keagan Schpfer
CC:beam@corp.sgi.com
Thanks for that Les (RC Pitstop's just down the road from me)! In the
spirit of a little local group support thing, here's my new photovore
circuit. I have a version which is suitable for solar power but got to do
some more tests. Note the (I think) unique photodiode "discriminator". It
detects the difference between photo diode leakage rates ie light level and
flips the output. Somewhat similar to a BiCore in behaviour but fewer parts
and only oscillates when the photo diodes are in balance. I use green LEDs
for photo diodes and they work fine. The complementary outputs of the
discriminator circuit are buffered with double 240 gates to drive one side
of each motor. The thing waggles towards the light as each motor is
alternately driven. The 1000pf feedback cap can be varied to
increase/decrease the left/right motor on times. These on times are also
dependent on light level. It makes for a interesting (ie complicated)
response to light conditions. The reverser is also kind of different : it
references the motor commons to +V or 0V and thereby reverses direction for
5 or 6 seconds when the feeler is closed. Pretty compact circuit design with
few components, suitable for small motors. The design was tested on a
breadboard with little camcorder gear motors. I will try a mobile platform
next. Feed(back) me!
Wilf Rigter
mailto:wilf.rigter@powertech.bc.ca
Subject:Re: Single 240 photovore.
Date:Sun, 11 Apr 1999 14:15:08 -0700
From:Sean Rigter
To:Chiu-Yuan Fang
Hi Chiu,
Sorry for the delay Chiu I thought I send this to you earlier but there
it was: in my draft directory.
Thanks for trying out the circuit! I just did a static bench test of
this design and I am very curious to hear if my predictions about it's
mobile behaviour will turn out correct. You have pointed out the most
interesting part of this design : I call it the High Low Oscillator
(HLO-pronounced "hello"?). It is a combination of the standard CMOS
oscillator, using an infinite feedback resistor, and a voltage
comparator with capacitive positive feedback.
The HLO is a gated oscillator with 3 states : 1) High - when the input
voltage is above the linear region, M1 is on, 2) Low - when the input
voltage is below the linear region, M2 is on and 3) Oscillating - when
the input voltage is in the ~2.3V to ~2.7V linear region, M1 and M2 are
both on with M1 speed proportionally higher than M2 when the input
voltage on the positive side of the linear input range. Actually, a
stable "linear" input range voltage is not possible since the HLO
oscillates and the input voltage waveform during oscillation is a
triangular wave with an amplitude of Vcc+1.2V.
The 100K pot input pot is optional used to limit current of sensitive
PIN PDs or LDRs and can be used to compensate for sensitivety. The pot
may be increased or elliminated with insensitve PDs like good old green
LEDs. The High and Low states are stable only under static conditions
but when mounted on a mobile platform the operation of the motors will
change the light level on the PDs and familiar phototropic behaviour
should result until the reverse switch is activated when, for about
10-15 seconds, the HLO becomes photophobic. The reversing circuit is
similar to a HLO to give a positive switching action and reduce power
dispation by switching as soon as the reverser input voltage enters the
linear region. The reverser output references one side of the motors
either to ground or Vcc, reversing the motor directions while the
reverser input is active low.
When the HLO is in the linear region more complex behaviour can result
depending on the interaction of the HLO oscillator and the light
feedback from the platform motion. The linear range is quite narrow and
by adding a 10M feedback resistor, the linear range can be extended but
the sensitivity and directionality of the PDs is reduced especially in
low light.
A HLO photovore with the positive PD and M1 on the left side and the
negative PD and M2 on the right should behave as follows:
When the PDs are not equally iluminated, the outputs are high or low and
the respective motors on or off. When the light falling on the PD is
roughly equal, the HLO oscillates causing the respective motors to run
at a speed proportional to the duty cycle of the outputs. If the light
level is low and diffused especially if the capcitor is larger (ie 0.01
to 0.1) or if the PDs are insensitive (ie green LEDs), the frequency
will be low and a shuffling motion will result. If the light is a low
level point source a long sweeping motion towards the light will risult.
If the light is brighter and diffused, the photovore will run in a wide
circle. If the light is a bright point source, the photovore will head
towards it in a straight line. When the
With a 1000pf cap, the frequency of during oscillation and the RPM of
the motors smooth and will be proportional to the PD ilumination
imbalance.
If the feedback cap is removed, the HLO oscilates at high frequency and
the circuit will draw 150 mA "dynamic" supply current. This is caused by
positive voltage feedback, capacitively coupled from output to input
shifted 180 degrees by the output R/C phase delay and propagation delay.
When the 1000 pF cap is installed, the 74AC240 HLO circuit current is
highest just before oscillation starts and draws about 3mA maximum in
addition to a maximum 100mA of motor current. The feedback cap of the
HLO may be increased to 0.01 to 0.1 uF for different (chunkier but
higher torque) behaviour and experimenting with a mobile HLO platform
will help determine the optimum value for a given application.
regards
wilf
Chiu-Yuan Fang wrote:
>
> This circuit is a gem for sure. One thing that confuses me is the function of
> the 1000pF capacitor. Without the cap, both motors tend to turn at once (much
> slower) when the light falls equally on the pd's. I'm a little confused and
> can't figure it out...I'm sure it's just some bonehead overlooked fact on my
> part.
>
> --
> Chiu-Yuan Fang
Subject:uPOPSE
Date:Mon, 29 Mar 1999 07:17:12 -0800
From:Sean Rigter
To:beam
The uPOPSEv2
wilf rigter 1999
Here is a 2.5V version of the micro power operational amplifier solar
engine (uPOPSEv2) This one uses commonly available 2N2222A output
transistors which happily saturate a 100-150 mA motor load. With higher
gain NPN transistors it will perform even better. The uPOPSE switches
on at 2.7V and off at 1.4V.
I tested the circuit with some 15 ohm Namiki motors using a simulated
solar cell from a 5V supply with a 100K series resistor. I also tested
this design with a couple of 45 ohm Sony lens motors. The circuit uses
a minimal number of parts but perhaps it can be further simplified. The
core element is the dual cmos opamp (TLC27L2) made by TI (Cdn $1.49).
Similar CMOS opamps should also work. The photodiodes are generic (5
for $1.99) with build-in IR lens. The absolute value of light current is
not that critical and a 100K pot is used to balance sensitivity. With
components shown, the circuit draws a constant current of about 5uA but
requires 50uA for base current at the switching threshold. A power
mosfet eliminates this threshold current for critical low light
applications. Total cost of all circuit components, not including the
solar cell or motors, is less than Cdn $4.00
The micro Power OPamp Solar Engine (uPOPSEv2) works as follows:
Summary
The basic circuit a threshold detector with hysteresis: the opamp output
switches positive and turns on the output transistor when the (+) input
is more positive than the (-) input (threshold) . When the transistor
turns on the (-) input is pulled to the 0V line reinforcing the
difference between the (+) and (-) inputs (hysteresis)
The transistor remains on until the voltage drops below about 1.4V when
the output turns off driving the (-) input more positive than the (+)
input and the cycle start over again.
Detail
When the main cap starts to charge, the voltage (Vcap) rises ,
rapidly at first and then slowing down as the charge approaches the
maximum available source voltage. This voltage appears at the transistor
collector connected to a 5M resistor with the other end connected to the
inverting input (-) of the opamp. The double inversion provides positive
feedback for hysteresis. In addition a 5M resistor is connected from
the (-) input to ground. This means the main capacitor voltage is
divided by 2 at the (-) input of the opamp which sets the trigger point
at Vcap /2. The capacitor voltage is also connected to the green LED
which acts as a "soft" zener with a 1V to 1.5V voltage drop at less than
1 uA . This means that the voltage at the (+) input is equal Vcap - 1.5V
near the upper trigger threshold and is equal to Vcap -1V near the lower
cut-off voltage. To be sure, the 100K pot and PDs modify this because of
the additional voltage drop across these components. At medium light
levels this additional voltage drop is small and is only used to
differentiate which SE should fire. The PDs have a effective impedance
of 10K to 1M and are connected to the cathode of the green LED through
a 100K resistor which is used to balance the sensitivity of the PDs.
Which SE fires first is determined how the current from the LED is
split in proportion to the light level on each PD. The PD current is
developed into a voltage across the 5.1M resistor to ground at the (+)
input of the opamp. When this voltage is slight lightly higher than
the(-) input the opamp switches the output positive and turns on the
transistor . Since the voltage at the collector drops to 0V, the 5M
resistor pulls the (-) input of the opamp also to 0V increasing the
difference between the (-) and (+) inputs and provides hysteresis
(lowering the switching threshold) The opamp output remains positive,
supplying base current to the output transistor, until the V+ of the
opamp falls below it minimum operating voltage (~1.4V) and the opamp
output impedance starts to rise cutting off the base current. When the
output transistor comes out of saturation for lack of base current the
(-) input rapidly rises to 0.7V (1.4V/2) and since (+) input is below
0.4V(1.4V-1V) , the opamp output switches to 0V holding off the output
transistor and the cycle starts again..
Subject:Re: 74HC240
Date:Wed, 31 Mar 1999 07:19:16 -0800
From:Sean Rigter
To:Benjamin Edward Hitchcock , beam
Hello Ben
Tri-state only refers to the "floating" or high impedance state of the
240 output. The inputs are NOT designed to sense 3 different logic
states. ie zero, one and floating. Always tie unused inputs to 0V or +V
or else your chip may get quite warm!
Tristate outputs can be connected together on a common bus with only one
output active (ie high or low) at a time. A bus of this type often has
termination resistors which pull up the bus when all outputs on the bus
are tri-stated. At 5V supply voltage, if you allow all 74HC240 inputs to
float, the chip could draw as much as 150 mA of supply current! Just
try tying all HC240 inputs together and to the wiper of a pot with the
pot connected across the 5V supply. Then adjust the pot for maximum
supply current through the chip and stand back. The same thing can
happen if you let the HC240 inputs "float".
This also means that quasi linear circuits like the microcore, bicore,
and other Nv neuron circuits draw substantial pulses of supply current
when the voltage at the input of the 74HC240 or 74HC14 enters the linear
region. Fortunately, the voltage is in the linear region for only a
short time but the supply current pulses can cause circuit to misbehave
(saturation etc) unless you provide adequate bypass caps on the supply
pins of the logic chips.
Long time constant Nu circuits like the PNC will draw high supply
current for a longer duration. Solar engines, which are in effect mono
Nu cores, can draw so much current when entering the linear operating
region (close to the trigger point) that the solar cell cannot supply
enough current and the charging of the capacitor stalls preventing the
SE from firing.
This high current also makes it difficult to design a 5V solar engine
using logic gates. The problem is much less severe at 2V supply
voltage, and this "linear region" current drops down to a few hundred
uA. This is one reason why the Steven Bolt's Sun Eaters circuits must be
operated at 2-3V. It is also the reason why a 5uA supply current opamp
designed to operate in the linear region is such a good choice for a
solar engine (nuff said).
enjoy
wilf
Benjamin Edward Hitchcock wrote:
>
> The 74HC240 is listed as a tri-state line driver.
> What does tri-state mean? High, low, and floating?
>
> Would it differentiate between two voltages that were very close to half
> the supply voltage like a normal 74HC14 chip does?
>
> What I mean is, what outputs are possible for values of input very close
> to half supply voltage.
>
> Thanks for any help,
> Ben
Subject:RE: adaptive walking gait?
Date:Tue, 6 Apr 1999 19:29:39 -0700
From:Wilf Rigter
To:"'beam@corp.sgi.com'"
Hello Grant,
A 180 degree phase shift of one motor (and one set of legs) would cause a 2
motor - 4 legged walker to reverse it's gait. Since this reversal is usually
caused by tripping a touch switch, there is a momentary condition caused by
this asynchronous phase reversal which interferes with the normal gait and
it will take a few steps to "center" the legs. This is normally
accomplished with centering springs connected from each leg to the body
which cause the legs to reciprocate around an average position at right
angles to the body. These centering springs provide the most significant
"feedback" and also help compensate for forces/losses which would cause the
legs to "drift" from their normal gait position.
Tuning of a walker means designing as much balance and symmetry into the
electronics and mechanics as you can before applying feedback.
Analysis of a 4Nv MicroCore (and BiCore) circuit shows that increased
loading of a motor (more pressure) will _shorten_ the duration of the
current through that motor. The reason is that the supply voltage drop
(under increasing load) and increased "motor noise" affects the active Nv
trigger point. The voltage drop and motor noise are coupled via a feedback
path through the power supply, the active high output mosfet of the previous
Nv stage and the active Nv input capacitor. This voltage drop and noise are
superimposed on the decaying capacitor voltage at the input of the active Nv
and cause the input voltage to cross the lower threshold earlier during a
negative noise spike or supply voltage drop. This shortens the duration of
the active "process" and the motor rotation.
Since the centering springs exert this kind of increased loading of the legs
at the end of each leg swing, shortening the process duration fortuitously
helps avoid excessive motor losses.
regards
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
Subject:RE: Linked BiCores; How Does The Slave Cycle?
Date:Mon, 12 Apr 1999 12:49:43 -0700
From:Wilf Rigter
To:"'Wouter Brok'"
CC:"'beam@corp.sgi.com'"
Very sharp Wouter!
Actually I send those waveforms to you privately but as long as we are
discussing them here I have attached them to this reply.You will find one
additional circuit which exploits the overvoltage at the input of the
"isolated" suspended BiCore to generate some additional supply voltages
(+7.5V and -2.5V).
The graphs are approximations I made with a CAD program. They don't have a
calibrated time axis. You are correct that the 74HC04 and 74HCU04 would have
the same exponential curve using the same RC parts but a different period
because of the difference in thresholds. The 74HC04 inverter has a voltage
gain of about 100 and a narrow (50mV) gap around 2.5V between the upper and
lower thresholds. The 74HCU04 inverter has a much smaller gain and widely
separated upper and lower thresholds. In this description, threshold means
the input voltage level at which the output voltage starts to change. The
graphs for the HC/AC240 are very similar to the 74HC/AC04 so the example
holds for both cases. However there are important effects related to output
load current and obviously the 74HC04 has much less current capability
(higher output impedance than the 74AC04 and 74HC/AC240. Power supply noise
and "ground bounce" can change the period of a master or slave BiCore by
50% which could be suppressed by good supply decoupling and supply bus
layout for more repeatable results. Of course, this all falls into the
category of "feedback" so you can explore ways to the modulate BiCore pulse
width in response to change in load by deliberately allowing a certain
amount of noise to influence the BiCore period. This is the way in which
BEAM design exploits electronic circuit behaviour on the edge of chaos
giving rise to such complex and surprising behaviour in BEAM bots.
enjoy
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411
> -----Original Message-----
> From: Wouter Brok [SMTP:w.j.m.brok@stud.tue.nl]
> Sent: Monday, April 12, 1999 12:07 AM
> To: beam@corp.sgi.com
> Subject: RE: Linked BiCores; How Does The Slave Cycle?
>
> Hello, again
>
> Actually, having a look at them I come up with a couple of questions:
> -In the circuit of the 'suspended' bicore you use the 74HC04 and the
> 74HCU04. I don't know what the difference is between them, but what
> suprises me is that the exponential parts in the graphs don't seem to be
> the same, while I assume the resistors and capacitors are. How is that?
> -Are the time-scales the same for all graphs?
>
> How do the graphs look for the 74HC240; I don't know how much time it
> costs
> to make them, but if it doesn't take much I would like to see them; or are
> they the same as any of those?
>
> Regards
>
> Wouter Brok
Subject:Slave BiCore operation
Date:Sat, 17 Apr 1999 11:03:58 -0700
From:Wilf Rigter
To:beam@corp.sgi.com
Hello to all BiCore fans,.
I wrote this description of the operation of a slave BiCore a little while
ago but forgot to post it. I know that some readers already know this stuff
but I thought you might enjoy reading it and especially the surprise ending
in the next post.
The attached GIF of a Master-Slave BiCore shows the relevant waveforms. The
description of the master BiCore was previously posted. Because of the
symmetry of circuit operation, the waveforms on the bottom side of the
circuit would be identical but "upside/down".
In normal operation the familiar Slave BiCore is a kind of complementary Nu
Neuron with feedback.
Assume a stable condition where:
The outputs of the master are 1 and 0,
the inputs of the slave are 1 and 0,
the outputs of the slave are 0 and 1.
Therefore the voltage across the slave coupling resistors (Vsr) = 0V and the
voltage across the slave capacitors (Vsc) = 0V. Now assume the master BiCore
has just flipped it's bits.
The master outputs are now 0 and 1,
the slave inputs are still 1 and 0,
the slave outputs are still 1 and 0.
Therefore Vsr=Vcc and Vsc=0V and the slave capacitors start to charge /
discharge through the "coupling" resistors. So far, no different from two Nu
neurons (integrators) delaying a step input by their RC time constant :
The slave inputs 1 and 0 charge towards opposite values and when either of
the slave inputs reaches the switching threshold at approximately 1/2 Vcc,
the corresponding slave output starts to switch from 1 or 0 to 0 or 1. Now
feedback occurs, which is quite different from the Nu neuron and more like a
Nv neuron:
When the first output changes, this change is capacitively coupled into the
other slave input and causes that input, already near 1/2 Vcc to cross it's
threshold which in turn causes the second output to change, which is
capacitively coupled into the first input. The second RC node with the
larger time constant plays no role in the timing of the slave BiCore and
the RC components can be eliminated. This positive feedback results in an
rapid voltage change at both slaves input towards the value as the
corresponding master outputs. During this rapid change, each slave
capacitor charge is "dumped" through the slave input protection diodes so
that the voltage across the caps and resistors rapidly changes to 0V. At
that point the following stable condition exists:
The master outputs are 0 and 1,
the slave inputs are 0 and 1,
the slave outputs are 1 and 0
Vsr = 0V and Vsc = 0V
The process repeats when the master BiCore again flips it's bits in the
opposite direction.
The formula for the delay time of a 74HC/ACxx Slave BiCore is approximately
0.7RC.
The time constant of the master BiCore is much trickier to calculate
especially when components are closely matched since the switching threshold
is close to 0V across the suspended resistor (ie on the flat part of the
exponential discharge curve). This is what makes the master BiCore time
constant long for a given RC and quite sensitive to preemptive triggering by
"feedback" from the load. A rule of thumb used for determining the 74HC/AC04
or 74HC/AC240 type master BiCore time constant is approximately 1.4RC. Based
on the requirement for 90 degree phase delay between Master and Slave
BiCores the same RC components can be used in both. The 90 degree phase
shift means that the Slave BiCore output changes occur half way in time
between the Master BiCore output changes.
enjoy
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411
Subject:AQUASENSOR
Date:Sun, 25 Apr 1999 12:33:33 -0700
From:Sean Rigter
To:beam
Hello everyone,
Introduction
Here is a simple but effective soil dehydration alarm circuit. Once the
threshold is adjusted for the specific plant and soil conditions, the
alarm will sound when it is "feeding" time.
It was inspired by Steven Bolt's Green Thumb project. The basic function
of detecting dry soil conditions is there but in a smaller more compact
circuit. Used with a 1.5 AAA or button battery it draws a mere 5uA and
15 ua when the beeper sounds. It works down to 0.8V with a lower but
still acceptable sound frequency and sound level. At which 1.0V, the
current consumption is only 0.5uA and 3 uA when the beeper sounds. With
such low current consumption the battery should last for several years.
The threshold is quite stable over the operating voltage and temperature
range because of the closely matched characteristics of the "same chip"
CMOS inputs which largely cancel out temperature and voltage effects.
This is a small improvement on the orignial since Steven Bolt uses two
chips with different input thresholds and this may make the threshold
setting sensitive to voltage and temeperature variations. The two 10K
probe resistors are optional but may help protect the circuit against
static discharge etc. Without "field experience", I can not tell you
that this device will promote plant growth however if anyone builds it
and keeps careful records (as Steven Bolt has done for his plant
experiment) this could be an interesting science project.
While this project is not, strictly speaking, related to Beam robotics,
the circuit uses a same "freeformable" single chip design which is the
hallmark of so many Beam circuits.
A micro power valve is next perhaps using some air pressure in the water
bottle to propel the liquid uphill. Stay tuned!
How it works
The design uses soil resistance as the parameter for determining the
threshold of insufficient soil moisture content.
The resistance threshold detector circuit consists of a RC bridge phase
discriminator. One RC leg of the bridge is used as an adjustable
reference time constant (TC-ref) while the time constant of the other RC
leg is determined the same value capacitor but an unknown resistance in
the form of the soil moisture probe.
Under wet soil conditions the "unknown" resistance is a low value
(>20Kohm) and the TC is small compared to TC-ref. The threshold of soil
resistance is detected by applying a square wave to the bridge network
and by detecting which TC is the longest. The detector uses a two gates
from the 74HC132 schmitt NAND gate as an RS flipflop with both outputs
Set high when the applied voltage is 0V and on the rising edge of the
applied squarewave, the flipflop input connected to the leg with the
shorter TC is Reset (low output) while the leg with the longer TC
remains set. The first input to go high (shorter TC) together with the
cross-coupled high output from the other side causes the output of the
first side to Reset and thereby inhibits resetting the other side
because of the crosscoupled low output.
The 1Hz square wave clock is a conventional one gate Schmitt trigger
type and the 1KHz audio alarm clock drives a Piezo type speaker. The
audio alarm is held off with a 1N4448 diode connected to the reference
side of the flipflop as long as the soil resistance is lower than than
the reference resistance. When the soil dries out out increasing the
soil resistance and TC to a value greater than the reference TC, the
reference output is reset and the alarm is enabled and generating a
pulsing beeping sound.
While this is a simple application for this circuit I have found that
this design can also be used to detect changes in capacitance and then
behaves like a proximity detector. Adding a bias resistor to the
"unkown" reistance leg of the bridge can provide a micro power voltage
threshold detector and the list goes on.
This intriquing simple TC phase comparator has much potential for other
applications (including microcontrolers such as the PIC Stamp which also
use a similar single slope conversion TC/D and A/D interface) and I look
forward to seeing this circuit pop up in other Beam designs.
enjoy
wilf
Subject:RE: AQUASENSOR
Date:Mon, 26 Apr 1999 19:11:26 -0700
From:Wilf Rigter
To:"'Steven Bolt'"
CC:beam
Thank you Steven,
Here's a single chip LED version. The LEDs must be high efficiency type.
With 3% duty cycle the average current is about 200 uA.
regards
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411
> -----Original Message-----
> From: Steven Bolt [SMTP:sbolt@xs4all.nl]
> Sent: Monday, April 26, 1999 10:44 AM
> To: Sean Rigter
> Cc: beam
> Subject: Re: AQUASENSOR
>
> On Sun, 25 Apr 1999, Sean Rigter wrote:
>
>
> Nice design, too. Using a Piezo did cross my mind at the time, but
> two LEDs - red to demand water, green to flash "all's fine" - were
> preferred by the `user group'. A device which most of the time does
> nothing might not be functioning. Given the two LEDs output
> requirement, a second IC is hard to avoid.
Subject:RE: Bicore head targeting?
Date:Tue, 27 Apr 1999 17:13:57 -0700
From:Wilf Rigter
To:"'Richard Piotter'"
CC:beam
Hi Richard,
The solution you are proposing is a solid traditional engineering approach
which will work just fine and my only suggestion for that design is forget
about the series diode, just integrate the two bicore outputs and compare
their average DC value which is 2.5V for 50% duty cycle with a window
comparator.
But your design is NOT BEAM (grin).
Here is a BEAM solution which was derived from my PD comparator in the
photovore circuit posted some weeks ago. It provides two LEDs to indicate
turning in the LEFT or RIGHT direction (seeking mode) and blinking LEDs when
the target has been acquired (balanced mode). The potentiometer should be
adjusted for mid position and when the target is acquired, adjusted until
both leds blink at about 2Hz. This is the indication for lock. For small or
slow changes in direction the lock indication continues since the error
signal is small. For faster changes or "unlocked" continuous turning
conditions (mind that you don't strangle you head), the left or right LED
will light indicating the direction of turning. This is just a thought
experiment, I have not build or tested this circuit but I'm sure it will
work as described. So if anyone out there is "quick on the draw" and builds
this circuit tonight, some feedback would be appreciated.
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411
> -----Original Message-----
> From: Richard Piotter [SMTP:richfile@rconnect.com]
> Sent: Tuesday, April 27, 1999 2:41 PM
> To: beam
> Subject: Re: Bicore head targeting?
>
> PERRRRRRRRRFECT!!!
>
> This is EXACTLY what a switching power supply does. It creates a pulse
> that can have a variable duty cycle. A filter (caps, inductors) filter
> it into DC
enjoy
wilf
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca