Testing

The following steps describe how to test your ANALOG THING thoroughly.

• Adjust the DVM and check the coefficient potentiometers:
  • First of all, set the mode control switch on the bottom right to OFF.
  • Connect THE ANALOG THING to a 5V USB power supply by means of a USB-A/USB-A cable.
  • Set the mode control switch to COEFF. In this mode the coefficient potentiometers can be set with the DVM showing the current value of any of the eight coefficient potentiometers COEFF 1..COEFF 8.
  • Set the COEFFICIENT switch to 1.
  • Set the potentiometer COEFF 1 fully counter clockwise. The DVM should now display zero (a slight deviation from zero is permissible, so a displayed value of 0.003 would be OK, too).
  • Now turn the potentiometer COEFF 1 fully clockwise.
  • Adjust R14 (right side of THE ANALOG THING) with a tiny screw driver until the DVM displays 1.000.
  • Check the remaining potentiometers by stepping the COEFFICIENT switch through positions 2 to 8 while setting each of the remaining potentiometers first fully counter clockwise and then fully clockwise. The DVM should display (nearly) zero and 1.000 in these two cases.

• Test the summers and inverters:
  • Set the mode switch to IC (initial condition).
  • The following steps are to be performed for each of the four summers:
    • Connect the jack labelled U on the front panel with one of the output jacks of the summer being tested. Connect one of the inputs with weight 1 with the machine unit -1 (lower left corner of the patch field). The DVM should display a value very near to +1.000.
    • Connect the -1 machine unit shortly with one of the summer inputs weighted with 10. The DVM must show a value in excess of 1.100 and the overload indicator OL should be lit.
  • Perform the first of these steps with each of the four inverters. (Do not connect -1 or +1 directly to the summing junction input SJ.)

• Test the multipliers (perform the following steps for each of the two multipliers available on the analog computer):
  • Connect the DVM to the output of the multiplier being tested.
  • Connect the two inputs of the multiplier with +1 and +1 and check that the DVM reads very near to 1.000.
  • Connect the two inputs of the multiplier with -1 and -1 and check that the DVM reads very near to +1.000.
  • Connect one input to +1 and one input to -1. The DVM should now read very near to -1.000.

• Test the comparators (perform the following steps for each of the two comparators):
  • Connect the >0 input with +1 and the <0 input with -1.
  • Connect the DVM with the OUT jack of the comparator.
  • Connect either A or B with +1 and then with -1. The DVM display must switch between near +1.000 and -1.000.

• Test the integrators (perform the following steps for each of the five integrators):
  • Make sure the mode switch is set to initial condition (IC).
  • Connect -1 to the IC input of the integrator.
  • Connect the DVM (the jack labelled U) with the output of the integrator.
  • Check that the DVM shows near +1.000. With IC connected to +1 instead, the DVM should read near -1.000. If this is the case, IC mode works.
  • Connect the jack labelled SLOW with OUT of the integrator under test, thus selecting a low time scale factor.
  • Connect the IC jack with +1, and connect one of the inputs with weight 1 with -1.
  • The DVM should now read near -1.000.
  • Set the mode selector switch to operate (OP). The DVM display should now increase quickly from about -1.000 to > 1.000 and the overload indicator OL will be lit.

A more thorough test of the integrators can (and should) be done with an external oscilloscope or a sound card "oscilloscope" as follows:

• This test requires two integrators and one inverter.
• Set the mode select switch to initial condition (IC).
• Connect the slow jack of each of the two integrators with an output jack of the very same integrator, thus selecting a low time scale factor.
• Connect IC of the 1st integrator (I1) to +1.
• Connect the output of I1 with an input with weight 1 of the 2nd integrator (I2).
• Connect the output of I2 with the input of an inverter.
• Connect the output of that inverter with an input with weight 1 of I1. (This circuit now solves the differential equation y″(t) = -y(t).)
• Connect the output of I1 with the jack labelled X.
• Connect the X output at the back of THE ANALOG THING with an oscilloscope or a sound card input (some oscilloscope software is assumed to be up and running on your computer).
• The oscilloscope should display a line at -1 (the output jacks are fed by a voltage divider so the actual reading is less than the machine unit voltage of -10V - this was done to avoid damage to an attached sound card).
• Set the mode selector switch to operate (OP). The oscilloscope will now display a rather low frequency sine curve.
• Set the mode selector switch back to IC and remove the two connections between SLOW and the OUT jack of each of the two integrators.
• Set the mode selector to OP. The oscilloscope should now display a sine wave with much higher frequency (factor 100) than before. (This signal's amplitude may increase or decrease over time which is normal and more or less unavoidable in a simple setup like this.)

The only thing left to test is the repetitive mode of operation:

• Turn the potentiometer labelled OP-TIME fully counter clockwise.
• Set the mode selector switch to REP.
• The LEDs OP and IC should be flickering.
• Slowly turning the OP-TIME potentiometer clockwise should cause the OP indicator light for longer and longer periods of time.
• Perform this test also with the mode selector switch in REPF (fast repetitive mode).