8
We can't use TNT or FedEx. If we retained the permanently installed lithium batteries, we might be able to
use DHL or UPS, but it would cost an extra AUD$200 or more per shipment.
So for all customers outside Australia we will keep using the Australia Post EMS service, with the new
memory backup arrangements described in the next section, which does not involve a lithium battery being
installed in the machine when we send it by air freight.
Measuring the voltage of the permanently installed lithium battery
This sub-section only applies to Devil Fishes with the Option A arrangement of a soldered-in CR 1/2 AA
cylindrical lithium battery.
To test the battery voltage, remove the Mode knob. (Use adhesive masking tape or rubber gloves to grip it, if
necessary.) Connect the negative lead of a digital multimeter in voltage mode to the ground of the machine.
The best way is to clip on to the ground of one of the 3.5mm jacks at the rear, or to plug a lead into any of
the sockets and connect to the ground of that lead. Note that the metal ring on the outside of the 1/4 inch
jacks is not grounded. Place the positive lead of the meter on the test point near the Mode Switch. This is
the lithium battery voltage via a 3.3k resistor. Any voltage above 3.0 volts is fine.
It is possible to erase memory's data, and allow the chips to power up with data determined by the physics of
each cell. This will result in "random" patterns. This can be achieved by turning off the machine, removing
the C-cell batteries, removing the Track/Pattern Knob and shorting to ground, for more than a second the test
point which is underneath the knob.
To measure the current drain of the memory system, turn the machine off, and remove any C-cell batteries.
Connect a micro-amp meter between these two test points. Current will take a while to stabilise due to the
presence of a capacitor on the RAM chips’ VDD (VRAM) supply. The final current should be less than
1uA.
4 - Option B - C-cells with under-voltage protection, a large capacitor and an
optional user-installed replaceable lithium coin-cell battery
This is the system we are using for all overseas customers. A variation of it for Australian customers is
described in the next section – Option C. Option B solves all three problems mentioned above for Option A,
and introduces one smaller problem: that if the user wants to have a lithium battery for backup, they will
need to open the machine (or get a technician to do so) and clip a 2032 20mm diameter, 3.2mm thick,
lithium coin-cell battery into a battery holder. The Material Safety Data Sheet (MSDS 2.001.005) at varta-
microbattery.com state that the 2032 contains 0.07 grams of metallic lithium.
Option A's problem 1 (the C-cell batteries being flattened by accidentally leaving the machine turned on and
running from batteries for many hours) is solved by an under-voltage protection system. The TB-303
already has a PNP transistor Q44 though which all the +6volt power flows, during ordinary operation. Its
purpose is to protect against the batteries or the external power supply being inserted with the opposite
polarity, without the loss of 0.6 to 0.7 volts in a diode, which would also offer this protection.
We install a new circuit which disables the drive to Q44 when the supply voltage (from the C-cells, or from
an external power adaptor, if one is plugged in) is less than about 5 volts. The TB-303 won't run from 5
volts or less, so this does not affect normal operation. It prevents the C-cell batteries from being flattened if
the machine is accidentally left on and running for extended periods. When the C-cell batteries have 5 volts,
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