Loading ...
Sorry, an error occurred while loading the content.

Re: [beam] SPSH with inverted 1381 SE

Expand Messages
  • Wilf Rigter
    I have attached a simple PSHEAD v1 schematic for a brief explanation. It still is the simplest and most elegant of the PShead designs. The actual component
    Message 1 of 9 , Apr 5, 2003
    • 0 Attachment
      I have attached a simple PSHEAD v1 schematic for a brief explanation. It
      still is the simplest and most elegant of the PShead designs. The actual
      component values don't matter very much as is explained below.

      The PD1/PD2 photobridge acts as a voltage divider with the midpoint at Vcc/2
      when the light on each PD is equal. The response is ;inear over a wide range
      of ambient light levels. Some PDs are very efficient and may need some light
      shielding (ie heat shrink) to reduce the photo current level in very bright
      light.

      The hi/lo oscillator is uses R1/C1 to set the basic frequency. Resistor R3
      connected from the photobridge midpoint to the R/C node of the oscillator is
      used to influence that frequency. That frequency depends on the voltage of
      the midpoint as well as the absolute resistance of the PDs. In general, the
      frequency is the lowest when the PD bridge center voltage is near the
      threshold of the 7AC240 inverter input.

      With a R1 to R3 = 10 to 1 ratio, the frequency and the duty cycle varies
      when the PD output voltage is less than +/-10% above or below the threshold.
      Voltage levels above and below that +/-10% range will cause the output of
      the oscillator to stop and will be steady high or low, inverted with respect
      to the input voltage. The band of oscillation can be made more or less by
      decreasing or increasing the ratio of R1 and R3 values. (ie if R1=R3 it
      always oscillates). I use typical ratios of between 2 to 1 and 10 to 1. If
      the ratio is high, the sensitivity is greater but the tendency to wiggle is
      also greater. Remember a shaky head is not power efficient.

      For some applications that have lot's of build in damping (ie Submarine
      head, Mazola head) R3 can be 0 ohm 8)

      The Nv/Nu driver (also called Nx driver) both differentiates and integrates
      the complementary outputs from the oscillator. When the oscillator
      oscillates, the Nx driver AC couples the output pulses noninverted as the Nx
      time constant is longer than the oscillator period. With AC coupled
      (non-inverted AC) pulses in phase across the motor, the PSHead is in the
      power save mode but with the brake on! That is important to be able to stop
      the motor rotation quickly to avoid mecahnical overshoot when the head is
      aligned with the light source.

      When the oscillator stops oscillating theres are no pulses to AC couple and
      instead, the steady output is DC coupled (and inverted) to cause a
      differential voltage across the motor which then rotates.

      The ratio of the R1/C1 and R2/C2 time constant should be about 1 to 10 for
      low standby power. Smaller ratios can be used for faster and more "varied"
      response but sometimes higher standby current. Since the R1/C1 time
      constant is influenced by R3 and the photo bridge output voltage, that ratio
      will vary with light level. The ratios of those two RC timeconstant
      component values cause a variety of behaviour, sensitivity and efficiency.
      For solar powered PS Heads, the time constant of R2/C2 should (probably) be
      much shorter than the duration of the SE pop or some unpredictable (perhaps
      interesting) side effects may occur.

      Hope that short description helps,

      wilf


      ----- Original Message -----
      From: "Mike Robertson" <mikerobe@...>
      To: <beam@yahoogroups.com>
      Sent: Saturday, April 05, 2003 6:55 PM
      Subject: Re: [beam] SPSH with inverted 1381 SE


      > all right
      > ver 1-2 is what i have built right now and it works seemingly quite well
      > but i haven't found any caps of the same values as those in your original
      > circuit
      > the two caps...do they control the on and off time? (off charge, on run)
      > if so then i could just drop the 10 M down to 100k and keep usign the same
      > caps i have right?
      >
      > maybe i should start working through other circuits and convert them to
      use
      > the inverted 1381
      >
      >
      > mike
      >
      > m
      > ----- Original Message -----
      > From: "Wilf Rigter" <wrigter@...>
      > To: <beam@yahoogroups.com>
      > Sent: Saturday, April 05, 2003 7:14 PM
      > Subject: Re: [beam] SPSH with inverted 1381 SE
      >
      >
      > > Hi Mike,
      > >
      > > Ori's suggestion is good.
      > > Some tiny comments:
      > > You're correct to switch the PDs with pin 1. Otherwise those can leak a
      > lot
      > > of current during charging.
      > > Leave pin 19connected to 0V as you suggested to avoid floating inputs.
      > >
      > > The right hand PD should be reversed. The 1uF cap should be 0.01uF and
      > the
      > > 0.1 uF should be 0.001uF to make the response time 0.1 seconds (With 10M
      > and
      > > 1uF the timeconstant would be 10sec!).
      > >
      > > wilf
      > >
      > >
      > > ----- Original Message -----
      > > From: "Mike Robertson" <mikerobe@...>
      > > To: <beam@yahoogroups.com>
      > > Sent: Saturday, April 05, 2003 12:53 PM
      > > Subject: Re: [beam] SPSH with inverted 1381 SE
      > >
      > >
      > > i wasn't exactly clear on what changes you meant
      > > but here's what i did
      > > 13812 out to pin 1 on XX240
      > > 19 stayed on ground
      > > 20 to Vcc
      > > 10 to gnd
      > > 13812 pin 2 to pin vcc
      > > 13812 pin 3 to pin gnd
      > >
      > > and the last inverter was added to the driver portion
      > > pin 9 to 7 (pin 1 to 9 removed)
      > > pin 11 to 13
      > > 10M resistor connecting pin 10 and 11 removed
      > > and cap values were changed
      > > ----- Original Message -----
      > > From: Ori
      > > To: beam@yahoogroups.com
      > > Sent: Saturday, April 05, 2003 1:16 PM
      > > Subject: Re: [beam] SPSH with inverted 1381 SE
      > >
      > >
      > > That will work just fine, but... An improvement from someone you
      > wouldn't
      > > expect (Wilf ;).
      > >
      > > Connect all of the parts as you would if the cap was a battery, except
      > do
      > > not connect the enable pins of your 240. Then, all you need to do is put
      > the
      > > 13812 in, and connect the output to the enable pins.
      > >
      > > Skip the solarengine! ;)
      > >
      > >
      > >
      > > ---
      > > Outgoing mail is certified Virus Free.
      > > Checked by AVG anti-virus system (http://www.grisoft.com).
      > > Version: 6.0.463 / Virus Database: 262 - Release Date: 3/17/2003
      > >
      > >
      > >
      > > To unsubscribe from this group, send an email to:
      > > beam-unsubscribe@egroups.com
      > >
      > >
      > >
      > > Your use of Yahoo! Groups is subject to
      http://docs.yahoo.com/info/terms/
      > >
      > >
      >
      >
      > Yahoo! Groups Sponsor
      >
      >
      >
      > To unsubscribe from this group, send an email to:
      > beam-unsubscribe@egroups.com
      >
      >
      >
      > Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
      >


      ---
      Outgoing mail is certified Virus Free.
      Checked by AVG anti-virus system (http://www.grisoft.com).
      Version: 6.0.463 / Virus Database: 262 - Release Date: 3/17/2003
    • Mike Robertson
      well needness to say the SPSH i built works well...i get about 10 to 15 degress of rotation per shot but now the disappointment....yet again i ve freeformed
      Message 2 of 9 , Apr 6, 2003
      • 0 Attachment
        well needness to say the SPSH i built works well...i get about 10 to 15
        degress of rotation per shot but now the disappointment....yet again i've
        freeformed the circuit modeled directly from the breadboard and the thing
        dont work right.... i get tiny twitches.
        I've compared every connection to the breadboard version at least 8 times
        and there are no mistakes and no shorts all components are the same value as
        the breadboard.

        i dont want to add this one to the pile of about 15 other freeformed
        circuits i've built that dont work...come to think of it every freeform i've
        done has failed to work properly or at all
        =(

        AAAAAAAAAAAAAAARRRRRRRRRRRRGGGGGGGGGGGGGGHHHHHHHHH!!!!!!!!!

        =p
        mike
      • Drew Brown
        Double check your chip orientation (position) Hit each connecton one more time with the soldering iron just to make sure you got good connections. Did you
        Message 3 of 9 , Apr 6, 2003
        • 0 Attachment
          Double check your chip orientation (position)
          Hit each connecton one more time with the soldering iron just to make sure you got good connections.
          Did you happen to overheat the chip while soldering it? (seems unlikely but possible)
           
          Sorry to hear you are having trouble freeforming.
          That's my personal favorite technique.
           
          DrewB
          ----- Original Message -----
          Sent: Sunday, April 06, 2003 10:40 PM
          Subject: Re: [beam] SPSH with inverted 1381 SE

          well needness to say the SPSH i built works well...i get about 10 to 15
          degress of rotation per shot but now the disappointment....yet again i've
          freeformed the circuit modeled directly from the breadboard and the thing
          dont work right.... i get tiny twitches.
          I've compared every connection to the breadboard version at least 8 times
          and there are no mistakes and no shorts all components are the same value as
          the breadboard.

          i dont want to add this one to the pile of about 15 other freeformed
          circuits i've built that dont work...come to think of it every freeform i've
          done has failed to work properly or at all
          =(

          AAAAAAAAAAAAAAARRRRRRRRRRRRGGGGGGGGGGGGGGHHHHHHHHH!!!!!!!!!

          =p
          mike



          To unsubscribe from this group, send an email to:
          beam-unsubscribe@egroups.com



          Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
        Your message has been successfully submitted and would be delivered to recipients shortly.