Nuts and Volts - March 2015

The construction of the stripboard circuit is very straightforward, so a list of instructions isn’t necessary. As usual, install the parts by starting with the lowest ones (the jumper wires), and work your way up to the tallest (the four-pin female header). However, there is one point that I should mention: The holes at B3 and B6 need to be slightly enlarged so that a header pin and a resistor lead will fit in the same hole.

A 1/16 inch drill bit is large enough — just be sure to drill the board with the traces facing up so you don’t tear out the traces around the holes.

If you prefer not to take this extra step, just cut the stripboard so that the traces include nine holes rather than eight, and move the four-pin right angle male header one position to the left.

When you’ve completed construction of the stripboard circuit, you can test it with the same program that we used in Experiment 2.

Figure 8 is a photo of my completed stripboard circuit, and Our USB-to-serial inverter circuit provides a simple and inexpensive way to power and program our PICAXE breadboard circuits with a single connection. If your primary computer is a laptop, it also enables the possibility of mobile project development. (I’ve actually worked on the hardware portion of PICAXE projects while commuting on the local railroad!)

Before wrapping up Experiment 3, there’s one final point that needs to be mentioned. If you use the inverted Prolific cable to develop a PICAXE project that will ultimately be powered by batteries (or any other power source), don’t forget that if you remove the USB cable and inverter board from your circuit, you will need to tie the processor’s Serin pin to ground (via a 100K resistor) in order for the circuit to function correctly.

Of course, the same thing is true for the AXE027, the FTDI cable, or any other programming connection.

Where's the Power Switch?

As I mentioned earlier, there’s no power switch on the USB-to-serial inverter board; to disconnect power from the breadboard, you have to physically disconnect the cable. I’m sure you’re wondering why, so let me explain.

The inverter board is part of a larger project that I’ve been working on recently. Back in the June 2010 Primer, I introduced the FTDI-based AxMate programming adapter, and for some time now, I’ve wanted to extend the AxMate concept so that it can work with a variety of USB-to-serial adapters.

Since all PICAXE processors require the serial programming data to be inverted, and (as far as I know) the FTDI cable is the only adapter that supports software inversion of the data lines, I decided to develop a two-board system which includes an adapter board containing the circuitry required by a specific USB-to-serial cable (e.g., FTDI, Prolific, AXE027), and an interface board containing the circuitry required by all USB-to-serial cables (i.e., a switch, an LED power indicator, and a bypass capacitor).