Review: Hobbybotics Hobbyduino Mini
June 13, 2011
Brooksware2000 (Curtis) nicely sent me a couple of ATMega 328 chips flashed with the Arduino boot loaders, since I had mentioned that I wasn't set up to flash the chips I had myself. He included an Arduino clone board he made, and asked me to let him know what I thought. And so I bring you a review of the Hobbybotics Hobbyduino Mini!
Curtis is already working on some revisions based on my feedback, and says he'd like me review the changes as well. I'll update this review if I get a chance to test out a newer version of the board from Curtis.
If you have questions or ideas, please post them in the comments.
The Hobbyduino Mini is a minimalist board for the ATMega 28-pin processors. I'm using the ATMega 328P-PU. Curtis says the board should function with the other 28-pin Arduino variants such as the older 168. The key is to verify pin assignments.
The compact size and bare bones layout make it a good choice for integrating to a larger project. The board itself is a "no frills" design.
For example, there is no LED included for pin 13 as you would find on an Arduino Uno or many others. A lot of clone boards include the LED for compatibility with the official Arduino boards, but then have a jumper do disable it. Why bother? If you want an LED on your project, you can put one in.
I have attached the schematics Curtis provided to me.
The board assembly uses SMD components and an IC socket for the ATMega processor. Through hole connections are used for the headers, IC socket, FTDI connector and power connector.
I know that Curtis used his DIY solder reflow oven to assemble the SMD components, and I must say that they came out perfectly!
The small form factor (88mm x 30mm) is nice, but unique. Given that there are SMD devices on the board, I aksed Curtis why he didn't go with an SMD version of the ATMega328 and really shrink the board down to something about the size of an Arduino Nano. I thought that aligning with an Arduino form factor might provide customers with some choices for shields.
Curtis says he is working on an SMD version, but notes that having the ATMega328 as a through-hole component makes it easier to replace chips as necessary. For instance, you can set up the board as an ISP and connect it to another Arduino board to program the bootloader onto a blank ATMega328. The board can be used as a prototyping board or in a finished project.
Curtis is also working on some breakout boards for the Hobbyduino Mini.
Another thing I noticed is that if you snap together two breadboards, the header pins on each side of the Hobbyduino Mini align with the holes of the breadboard. So if the board was installed with extra long pin female headers instead of normal ones, you could use it with two breadboards for prototyping. This seems like a useful feature for prototyping.
The board can be powered from the USB port through an FTDI cable or from the external power connector.
The external power connector feeds an AP1117 Low Drop-Out (LDO) SMD voltage regulator capable of supplying 1A. The specifications say that the dropout should be less than 1.4V at full current load. I tested without any load other than the ATMega itself. The 5V output began to dip at about 6.2V, so that is performing to specification. The AP1117 has a maximum input of 18V. I left it running for several minutes at 9V input, and it didn't get warm, but I didn't want to test for the upper limits of the input voltage.
I've included the data sheet for the AP1117 as an attachment.
A 5V power and ground pin was broken out on each of the two digital and the one analog interface header. A forth header included no less than three each 5V power and ground connections, which can be very convenient.
There are 10uF electrolytic capacitors on the input and output of the voltage regulator, and a 0.1uF ceramic capacitor on the output. The 10uF capacitors are rated up to 50V since the input voltage to the voltage regulator is rated at 6.4V to 18V.
An small red LED indicator for power is included, positioned right next to the power connector.
All the interface pins are broken out on 8-pin female headers. Two digital and one analog interface headers each have six I/O pins plus 5V and ground.
A forth 8-pin female header has the RX and TX pins (which are also Digital pins 0 and 1). These pins are labeled RXI and TXO.
A nice feature is that along side each 8-pin header are through hole contacts for each pin. This makes interfacing to the board much easier.
The board is very nicely and clearly labeled white on green. A pinout list for the ISP pins is provided as well. I do have a few nit picks on the labeling (see 'Nit Picks' below).
The board size and parts count are kept small by leaving off the USB to serial translation circuitry you get on a Duemilanove or Uno. So to program the board, you need an FTDI to USB cable.
I tested the board by uploading the example blink sketch included with the Arduino IDE, and it worked fine.
The board includes a reset button, which is well placed and easy to reach. The board also auto resets after programming.
The left-hand pin (as pictured below) has a square contact pad, rather than a round one.
I assumed this indicated the ground connection, or Pin 1 for the FTDI cable. However, this was not the case. I had to invert my FTDI cable to get it working, so ground is on the right-hand side of the connector.
I couldn't see that the FTDI pins were labeled (see nit below under 'Labeling'), because the labels are covered by the 90 degree pins on the board. It is very easy to plug a connector in the wrong way.
Curtis agrees that he needs to label the FTDI pin connector better. The pinout arrangement was designed for the Sparkfun FTDI basic board [http://www.sparkfun.com/products/9716] so, the pin out arrangement mirrors that design. He intends to fix the labeling on future boards.
The pins for the FTDI connector are not labeled clearly, so you have to guess which way to connect the cable.
It would have been nice if the Digital 0 and 1 pins were labeled as such, in addition to their functions as RX and TX. I can see there was not a lot of room on the board for this, so the omission is pretty understandable.
On the power connector, the + sign for positive voltage will likely be covered once you install the power connector. If a keyed connector is used, this may be no problem, but it would be nice to be able to see the markings clearly just in case.
Curtis also says he will fix this. Even with a keyed connector, he finds himself flipping the board up to see which of the pins is the square pin (positive). In fact, the next board design will have a diode included just in case someone accidentally reverses the input power. "We don't need any magic smoke getting out," he says.
The board as provided to me for evaluation was missing the power connector and ISP pins. Curtis tells me he had intended to send connectors along with the board, but forgot to include them in the box.
How can I get one?
I asked Curtis if he intends to sell the board, and how it would be packaged.
Curtis says that he had not really thought about selling the boards at all, but intended to release the design as open source. He can offer the boards for sale if people are interested, so let him know.
He would offer them as fully assembled, partially assembled and as a kit (for the brave at heart). The partially assembled version would come with the SMD components already soldered to the board along with a mix of connectors.