ritual prototyping examples

Differential Amplifier

This example is a differential amplifier, using one half of a dual op-amp SOIC.

The alternating pattern of power and ground pads through the middle of the board allows for easy connection of the device. An 0603 size decoupling capacitor fits horizontally between the pads.

Along the top of the board is a row of distribution pads, where each distribution pad is surrounded by a ground pad to the top, and signal pads to the left and right.

The output of the circuit is taken to the cross-board connections on the left. These connect to horizontal tracks on the bottom layer that run horizontally across the board. We use a pin header on the right of the board to connect the overall module.

The arrangement of alternating pads allows us to complete the circuit using bare wire and solder bridges, without needing to jump over existing conductors.

Cross-board connections

There is a cross-board connection for each through-hole on both the left and right edges of the board. If we put a pin-header in the through-holes, then there is one cross-board connection for each pin. The cross-board connections lead to a common layout where application circuits are built on the left of the board and utility circuits like decoupling and regulation are built on the right (or vice-versa).

Voltage Regulator

On the right of the board is a voltage regulator (AP2112) in a SOT-23-5 package. We have added a pin header in the right through-holes and connected both left and right pins in a row to make it easy to plug into a solder-less breadboard. The input voltage Vin is distributed to both the Vin pin of the regulator and the enable (EN) pin. 

The pads on the far right (and left) edges of the board are commonly used for status LEDs. From the cross-board connection pad there is space for a 0603 current limiting resistor as well as an 0603 LED.

Rail configuration

On the under side of the board there is a diamond pattern to help configure the horizontal rails. The spacing of the pads means that any two horizontal rails can be connected with bare copper wire, rather than needing insulated wire to avoid shorting the wrong pad.

In this example we have connected the central ground rail to the outer ground ring. We have also taken the two inputs for the differential amplifier from the second and third pins of the header, counting from the top.

Passive Component Sizes

Size 0603 passive components work the best as fit between the pads both horizontally and vertically.

Larger sizes like 1206 and 0805 fit horizontally and we often use size 1206 indicator LEDs.

Smaller sizes 0402 and 0201 also fit on the board but are more trouble to work with. Resistors of size 0402 and 0201 do not have their values printed on them. Components of size 0201 are difficult to manipulate by hand.

TO-252 (DPAK) Layout

Package TO-252 (DPAK) fits horizontally on a ritual A board, but not vertically as it is too tall.

Package TO-252 (DPAK) fits horizontally as well as vertically on a ritual W board. Five legged versions such as the voltage regulator on the right fit without requiring jumper wires, provided one of the outside legs is bent to connect it to a pad on the side (as shown).

Jumper Wires

It is not always possible to build a given circuit in a single layer with just bare wire and solder bridges. If there is not enough board space or connection resources then we must resort to soldering in tiny insulated jumper wires, like the blue Kynar (PVDF) wire above. This is the same circuit as in the first example, but we have compressed the layout into a smaller horizontal space, at the cost of requiring the output signal to be wired out.

The design of hexapod prototyping boards reduces the need for these insulated jumper wires, and allows more of the circuit to be built with bare wire and solder bridges. Jumper wires are sometimes necessary, but they are always unfriendly for a variety of reasons:

• we need to cut and strip the insulated wires individually. It is much faster to pre-cut a pile of bare wires to a variety of useful lengths (1, 2, 3, 4 .. mm etc) and store them in a pill case ready to use (which is what you should be doing already)
• jumper wires tend to break after being wiggled, sometimes after only 3-4 wiggles. Bare wire soldered down to the board is as mechanically sound as a real PCB trace.
• Kynar insulation melts at 177C, but lead-tin solder melts at ~183C, and the iron temperature is typically 260-300C as it must be hotter heat the pads and component legs. If we accidentally touch a bare copper wire with the iron it is usually unharmed.
• jumper wires make it harder to clean the board of flux, dust, and other residue. If there are only SMD components and bare wires then we can spray circuit board cleaner over whole board and take to it with a brush. It is much harder to clean under arch-shaped jumper wires like the one above.

Time spent planning how to lay out a board to reduce the need for insulated jumper wires is always paid back when more of the circuit can be built without them.