Open heart surgery

OK, maybe not as dramatic, but it was just as vital.

With my final project deadline extended a week, I took a couple days of downtime to catch up on sleep. The all-nighters were adding up. Now I’m back and making some minor changes and a few fixes. Hopefully the thing will drive in reverse without catching on fire. If you don’t hear from me, send help.

Firmware for the not has been fleshed out and I’m looking forward to getting it coded. The loop is simple, checking the status of each input and setting a flag. That flag is passed to the three output functions, which run after the input stage. One exception is the turnaround() function, which is called by an interrupt on the whisker pin. Some output functions call themselves to complete a series of drive commands, for instance. This keeps things simple.

More to come.

All together now

Late night testing

Motor driver board

Mounting at the rear, near the motors, his board is centered around a SN754410, a quad half bridge driver. The IC includes clamping diodes, but external Schottky diodes add an extra layer of protection from potentially ruinous flyback current.

Power supply board

Power supply board for my two wheeled robot. 5 and 3.3V provided by TI LDO regulators at 3A each, and fused vbatt for the motors. PPTC rated 3A IH at 12V. Protection from over voltage condition (important when combining motors and MCUs) using crowbar circuits. Divider and space reserved for a tiny85 to monitor battery voltage.

The rats nest is burning

So testing on the first iteration on this board ended in a fit of curses too salty to repeat here. Decided to make another attempt, and incorporate the (painful) lessons from my first try. Opted for non-bussed perf board, and arranged components so their leads could be used to make connections.

Much neater rats nest on the flip side. Watch this post for updates on how this tests out.

This weird part could be inside your Sorny television

Ever heard of Bonens? Me neither, but these multi turn trimpots are very cheap. This apparent Bourns knockoff failed, so I removed it from the board and replaced it with another. Time for more testing!

Testing whisker front end module

Last night, I soldered my voltage comparator circuit onto a small protoboard for my EE40LX final project. The circuit is a window comparator, and allows adjustment of the flex sensor’s divider, as well as one side of the window. This allows for adjustment on install and over time, as resistance may change with wear.

Crowbar circuit for over-voltage protection

Over-voltage protection for each rail of my project’s power supply in the form of a thyristor (silicon controlled rectifier or SCR) based crowbar circuit. The Zener breakdown voltage determines the cut off and trips the gate of the SCR, causing a short condition. The short is then handled by a fuse, protecting sensitive devices. A threshold of about 1V for the Zener diodes (4.3V for the 3.3V rail & 6.2V for the 5V rail) was selected to allow for overhead in case of transient spikes.

Power blocking front end for analog IR proximity sensor array