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Propeller Education Kit - 40-Pin DIP (#32305)
PE Platform Circuit Enhancements
The following material has been added to the Propeller Education Kit Labs: Fundamentals text v1.2,
Setup and Testing chapter, just before the Troubleshooting section. It includes optional additions to the
40-pin DIP version of the PE Platform circuit. While the basic circuit is adequate for the experiments in
the book, the optional additions make it more robust and are recommended for more demanding
applications. CAUTION: THIS DOES NOT APPLY TO THE PROPSTICK USB VERSION.
Propeller Supply Voltage Regulation Its Important!
A stable voltage supply is important because many different application circuits and subsystems depend
on it. Any voltage supply fluctuations will translate directly into fluctuations in 3.3 V high signals sent
by Propeller I/O pins. They also translate into fluctuations in Propeller I/O pin threshold voltage, which
in the Propeller is approximately of the 3.3 V supply voltage. When voltage is applied to a Propeller
I/O pin set to input, the Propeller interprets it as binary-1 if that voltage is above the threshold or binary-0
if its below. Propeller I/O pin high and low signal levels and input threshold voltage are also used in a
variety of analog to digital (voltage measurement) and digital to analog (voltage synthesis) applications.
So any supply voltage fluctuations that affect output-high and input threshold voltage levels also reduce
the accuracy of both voltage measurement and synthesis.
Products and prototyping printed circuit boards designed with Propeller chips typically have several
features that improve supply voltage stability. The voltage regulator output is usually very close to the
Propeller chips supply inputsthe 3.3V and GND pins. Depending on the diagram, you might also see
them labeled Vdd and Vss. The metal traces on the board that connect the voltage regulator to the
Propellers supply inputs are also typically wider than other traces that transmit signals. Since even metal
conductors have a small amount of resistance, these measures minimize the resistance between the
voltage regulators output and the Propeller chips supply inputs. This in turn improves supply voltage
stability by minimizing voltage fluctuations that can occur if Propeller current consumption fluctuates,
which can in turn occur when processors boot and I/O pins that drive loads switch on and off. Capacitors
can also be connected across the Propeller chips supply inputs to provide additional protection from
voltage fluctuations and further improve supply voltage stability.
Improve PE Kit Supply Voltage Stability
In comparison to products and prototyping boards, the distance between the voltage regulator output and
the Propeller supply inputs is quite large and can reduce voltage stability at the Propeller chips supply
inputs. Thats bad. The remedy is simple, and only requires two capacitors and two wires. Thats good.
The wires connect the supply inputs on opposite sides of the chip to each other to ensure that the supply
voltage levels are identical at both input terminals. The capacitors are placed across the 3.3 V and GND
supply input terminals on both sides of the propeller chip to filter out any voltage fluctuations caused by
the long supply lines.
Copyright Parallax Inc. PE Kit 40-pin DIP (#32305) v1.0 6/17/2010 Page 1 of 2 Parts List:
(1) Built and tested PE Kit Platform - 40-Pin DIP version
(2) Jumper Wires
(2) Capacitors 0.1 F
Procedure:
Figure 3-6 shows the jumper wire and capacitor connections. The Propeller chips 3.3 V supply pins are
connected to each other with one jumper wire, and the GND pins are connected with a second jumper
wire. 0.1 F capacitors are then connected across the 3.3 V and GND pins on both sides.
3 Disconnect power and programming port
3 Trim the two jumper wires to reduce any excess wire length when connected as shown in Figure
3-6 .
3 Use a red jumper wire to connect (J, 22) to (D, 19).
3 Use a black jumper wire to connect (J, 20) to (D, 22).
3 Plug the leads of one 0.1 F capacitors into (K, 22) and (J, 19).
3 Plug the leads of the other 0.1 F capacitor into (B, 19) and (B, 22).
3 Double-check your wiring.
3 Reconnect power and programming port.
Figure 3-6: Supply Input Strap and Filter Capacitor Connections for 40-Pin DIP PE Kit Platform
Copyright Parallax Inc. Product Name (#???-?????) v1.0 6/17/2010 Page 2 of 2