- The first is an applet embedded alone in a page; and the user enters an arbitrarily long string to describe the circuit as viewed at the input port. [See the source or a local copy at broeders/Broeders1.html.]
- The second is driven from a JavaScript panel where string input is replaced by data input which restricts the circuit to no more than three elements where the three are R, C, L. [See the source or a local copy at broeders/Broeders2.html .]

The Broeders applet can be found at various sites:-

- Workpage of Harry Broeders
- Wolfgang Christian at Davidson College.
- This site has both versions. [Select the
*package*named*impedance*.]

*Exercise*. What are the code steps from the input to the output of ParSer II and Broeders' applet?

*Exercise*. Here is a circuit which was designed to have an impedance flat over five octaves of freqency. Read the expression from the circuit and input it to Broeders' applet.

- You may wish to check your expression for the impedance of the circuit against my expression:-

`L(44E-8)+R(262E0)+(C(338E-12)//R(469E0))+(C(954E-12)//R(207E0))+(((L(146E-8)//(C(364E-12)+R(9E0))+R(115E0))R(115E0)+(C(333E-12)//(R(168E0)+(L(358E-6)//R(669E0))+(L(111E-6)//R(382E0)))`

I have yet to find my error. - The source of the circuit is Cal Coopman's article on Fractors and the Fractroller.

*The first thread*:-

- In the late eighties one of my languages was Smalltalk. I found that I could create an
*infix*operator. For example, I could already write 3 + 4 for the sum of two resistors in series. But, further, I could define, say, # to be the operator for expressing the sum of two resistors in parallel as 3 # 4. The result was that I could write the resistance between a port node of any size circuit as an expression (just like a mathematical expression, with the new operator). [Incidentally, such a circuit must have the*series/parallel*structure.] - When I began teaching
*Internet Programming*in the late nineties (in HTML/JavaScript) I found that I could NOT invent a new*infix*operator. So, for series/parallel resistors as a topic, I replaced 3 + 4 with a function*s*(3,4) and introduced a function*p*(3,4), and rewrote the resistance between two nodes in terms of these functions. The calculator for series/parallel resistors was followed by a calculator for series/parallel RLC-circuits where impedance between the input nodes was calculator for an applied*cosinusoidal*voltage with given*frequency*. - This year I have come across Harry Schroeder's applet (in Java) which uses + and // as infix operators). Harry Schroeder created his applet in 1997, which
*graphed*the magnitude of the impedance between the input nodes as a function of the frequency of the applied cosinusoidal voltage.

- When teaching HTML/Javascript in the late nineties one of my hypertexts included three chapters on Java. In the first chapter an applet was introduced to be simply embedded with no knowledge of Java. In the second chapter the applet could be intitialised HTML (via
`param`) with some knowledge of the variables of the Java within it. In the third chapter the applet could be*driven*by JavaScript (via an HTML form) with some knowledge of the methods of the Java within it. [As an addendum: one question in the Semester Examination would ask the student to make a minor modification to the Java code to allow JavaScript to drive the applet in a particular way.] - While I was thus working in the late nineties I came across the work of Wolfgang Christian at Davidson College where he had done, and has continued to do, so much work on
*Physlets*which feature the interaction between JavaScript and a Java applet. I was pleased to introduce Wolfgan Christian's*Physlets*to my students.

Wolfgang Christian at Davidson College:-

- Physlet Resources: note the list of contents (for example "physlet_resources/bu_semester2").
- Documentation and Physlets documentation. [But see documentation, with examples, at this site.]
- Applets includes Broeders impedance calculator and:-
- Resistors.
- Capacitors.
- Phys 230L: Broeders' applet driven by an RLC-circuit (via JavaScript).
- Copurse material.