Confessions is a series where we share prototypes that didn’t quite work out. Read previous posts for the Bus Pirate, #twatch, and web platform here.

The USB Infrared Toy took a few tries to get right. We’d like to fill you in on some things that happened behind the scenes before we released the v1 hardware. It went through three revisions before we were happy, and even then there were plenty of bugs in the initial production version.

The USB IR Toy is $20, including worldwide shipping. At the time of this post it’s on back order, but v1a hardware is currently in production.

Continue reading for a look at the early USB IR Toy prototypes.

The first IR Toy prototype had a PCB USB connector ‘tongue’ (seen here). We weren’t sure it would work, so we also included a regular through-hole USB jack too. This was a good move because the PCB we used was too thin to make good contact with the USB port.

A circuit based on outdated datasheets was used for the IR receiver. C4 is a 10uF capacitor, and R2 is a pull-up resistor for very old-style receivers that don’t have one internally.

In this version the PIC drives the IR LED directly without a transistor. The MCLR circuit uses a SOT-23 diode (D1).

An SMD mini-B USB jack was used in the second prototype instead of the PCB and through-hole USB connectors.

The power supply for the IR receiver was updated based on a modern datasheet, and the external pull-up resistor was removed. Part layout at the front of the board was cleaned up a lot.

We decided to try an interrupt pin with a Schmitt trigger to give the receiver better noise immunity. The white wire was added so we could test the new interrupt before committing to another PCB.

Version 1 is a fairly major update from the last prototype.

We connected the IR receiver to both interrupt pins. The current firmware uses the pin with a Schmitt trigger, but the TTL pin is also available for experimentation.

The MCLR diode was changed from an SOT-23 package to DO-323. This change saves some space and reduces the pin count.

We also really wanted the IR LED to be hackable for higher current. The PIC pin can only source 20mA max, so we added a transistor that can handle up to 200mA.

This is the initial production version. It has one major error: the IR LED silkscreen is backwards in the Eagle library. The small tab pointing up and to the right should be on the bottom left. Preorder 1 shipped with the LED backwards, this was corrected in preorder 2.

Version 1a is a minor manufacturing update. The latest files are available in the SVN.

Current back-orders, and future orders, will be filled with v1a hardware.

This version uses a ‘normal’ LED footprint instead of the funky, incorrect SFH-482 from the Eagle part library. We requested that Seeed use a plain IR LED like we used in the prototype, instead of the dated (and expensive) SFH-482. This version will also ship with a 180ohm current limiting resistor for higher-power IR LED transmission.

Onwards

Without a doubt there will be future revisions of the USB IR Toy hardware.

• We have an all through-hole kit version ready to go.
• The IR transmitter could be replaced with a proper right-angle module instead of a bent-LED.
• Most of the IO pins are unused and should be brought to the edge for prototyping and expansion.

You can continue this discussion, ask questions, and make suggestions in the USB IR Toy forum.

The USB IR Toy is $20, including worldwide shipping. At the time of this post it’s on back order, but v1a hardware is currently in production and should ship soon.

Last week we released the #twatch v2, an ethernet backpack for 20×4 character LCDs. This wasn’t the only version of the #twatch that we designed. V2 is based on the slick, inexpensive, single-chip ethernet microcontroller, the PIC 18F67J60. The biggest downside to the 18f67J60 is that it can only be programmed an average of 100 times. The limited program cycles make it really difficult to develop the firmware unless you’re a programming genie.

#twatch v1 is a development board for the #twatch firmware. It uses a PIC 24FJ64GA002 microcontoller with a million potential programing cycles, and an ENC28J60 for ethernet access. The design isn’t as advanced as v2, but it’s key to developing the #twatch firmware. We also use the v1 #twatch to diagnose new bugs, like the recent change in Twitter JSON.

You can buy an assembled #twatch v2 PCB for $30, including worldwide shipping. Keep reading for more about the v1 design.

Hardware/PCB

#twatch v1 uses a 28pin SOIC PIC24FJ64GA002. This is one of our favorite chips, you might recognize it from the Bus Pirate.  These 16bit chips are really easy to work with, and they have a ton of RAM for storing Tweets. Most importantly, it should last through a million program cycles, so it won’t burn out during development like the 18F67J60.

Since the 24FJ64GA002 doesn’t have a built-in ethernet transceiver, we used the 28pin SOIC ENC28J60 ethernet controller.

The 24FJ64GA002 doesn’t have enough 5volt tolerant pins to operate the LCD in 8bit parallel mode, so we used the 4bit mode instead. Most LCDs have a 4bit mode, but it cuts the refresh rate in half and makes the scrolling seem a bit jerky.

The LCD screen and ethernet transceiver can use a lot of current. Depending on the power supply, the voltage regulators may have to dissipate a bunch of heat. The v1 #twatch used surface mount SOT-223 regulators, but we decided to use larger TO-220 regulators on v2. Additionally, there’s some really poor routing and sizing of power traces on the v1 PCB.

v1/v1b

V1 (image) and v1b (rendering) are slightly different versions of the same board. V1 uses a 10mm through-hole potentiometer, v1b uses a small 3mm surface mount version. V1b has cleaner routing around the backlight control, and uses a larger 1206 current-limiting resistor.

Conclusion

The PCBs and firmware for #twatch v1 are on the Google Code project page. If you want to build your own v1, Seeed has our extra PCBs, and we’ll be giving away free v1 and v2 #twatch PCBs for the next few Free PCB Sundays.

You can order an assembled v2 #twatch for $30, including worldwide shipping, until September 23rd, 2009. Your support makes our projects possible, thank you.

The original web server on a business card Ian posted at Hack a Day was a homemade single-sided PCB with a few jumper wires. A version 2 was designed on a professional PCB, which opened up a lot of possibilities for new features. We added a 128×128 color Nokia knock-off LCD to make a network-connected photo frame.

The blue wire on the left connects some power pins we forgot to route. The unrouted wire was directly over the connecting wire, which made Eagle Cad’s unrouted indicator invisible. Now we use the zoom-unrouted.ulp script to check for unrouted wires before submitting Gerbers to the board house.

This design remains unpublished because the parts are hard to find. SparkFun stopped carrying the microSD card holder, and a new batch of LCDs didn’t work the same as the old models. The giant DPack 3.3volt regulator (LD117) next to the power jack at the back of the board was also a really expensive, somewhat rare part. We have one extra PCB that we’ll give away on a future free PCB Sunday.

The Bus Pirate V2a and V2go weren’t the only design candidates for the Bus Pirate v2 series. Here’s a rendering of the Bus Pirate ‘v1.5′, a design that never saw the light of day. This Bus Pirate was meant to be completely portable. It has an LCD to display the terminal, and a keyboard jack to work with a roll-up rubber keyboard.

Here’s some of the differences between this version and the final v2 series.

1. This design didn’t include software controlled pull-up resistors. It uses the jumper concept from v1a with SMD resistors.
2. V1.5 included a Nokia LCD knock off, like the one SparkFun sells for $15. The LCD backlight needs 7volts, so the large SOT223 regulator behind the power supply is a LM317 set to 7volts. The LM317 also supplies the other regulators with 7volts, which is better than the 5V supply to 5volt regulators on the v2a and v2go.
3. The six hole pattern seen on both sides of the PCB is for the PC keyboard connector. PC keyboards operate at 5volts, so this feature took two of only seven 5volt tolerant pins on the PIC24FJ64.

When we decided to manufacture the Bus Pirate, this design was too complicated and expensive. The code to run the LCD terminal and read the keyboard was big and made it hard to add new protocols. The knock-off Nokia LCDs are really inconsistent too, even different batches from SparkFun require different drivers. We minimized the design first to the v2a, then to the v2go.

In the end, we’re really pleased with the v2go. In retrospect, however, there were a few changes that would have make the whole process smoother. These have been integrated into the updated Bus Pirate v3, which is an even cleaner design that should be easier to manufacture in quantity.