And... new blog location is up

blog.awkwardengineer.com is now connecting to tumblr. good bye, blogger. you were good to start...

Saying Goodbye to Blogger

To those who still get this RSS feed or read blogger, I've decided that the platform has become quite dated and will be switching to tumbler. I'm a little sad that Google let blogger die, but it's time to move to something that a bit more modern.

Best regards!
-Sam

It's not how many times you get knocked down, it's how many times you get back up.

It's not how many times you get knocked down, it's how many times you get back up. Two years ago, my first Kickstarter failed, and it was a shitty, shitty feeling. I dusted myself off, learned from it, and got back at it with Kickstarter #2. Over 500% funded with a full week left to go. If you have friends who like geeky stuff, please share.

https://www.kickstarter.com/projects/1080427607/awk-105-analog-voltmeter-clock

Milestone Reached!

Guess what! We hit a major milestone with the Analog Voltmeter Clock! Working, custom circuit boards! To celebrate, we'll be drawing three names at random from our email list and giving the winners a choice of any item from the Awkward Engineer Store. 

The Technical Stuff:

(scroll to end for pics)

I've been told that nobody get's their first printed circuit board right, there are just too many tiny details that could go wrong. I was pretty nervous waiting for my boards to come back (I ordered 5 populated prototypes) and had a couple scary moments, but all in all, everything went pretty well. Here's the run down of what happened:
I messed up an easy one, right off the bat. The holes for the screw terminal mounts that attach the meters to the board were sized for a 2mm screw, not 2.5mm. A couple minutes with a drill solved that problem. Luckily, there was still enough plating around the screw hole that I still could get electrical contact.

The pinouts on the PCB were different than the pinouts on my breadboard prototype. I slapped my forehead pretty hard, but then it was a quick fix in firmware. Fortunately, the ISP header was wired up the right way and I could still flash the chip's memory.

The firmware was written for the 20khz crystal I had on hand to build the breadboard. Again, a minor fix in firmware to change to the 32.768khz clock crystal.

The voltage divider on the board was designed to work with the potentiometer "mode" knob and an optional unpopulated "alarm" switch. (Future versions only...). One more fix in firmware was need to get the levels right for the different modes.
The working clock! Running off an AA battery for about 2 weeks now!




The populated side of the board.

The board/meter screw terminal interface.

What's next?

Well, at this point, I feel like I've cleared all technical milestones and it's on to final pricing, campaign, and launch planning. The launch list (that means you guys!) is at a reasonable size for a small batch, so it's really up to me to pull the trigger.

Here's an example of what's still on my mind: Getting a custom meter scale ordered from the factory has a setup cost that needs to be defrayed by a couple hundred orders... or if I do a really small batch, I can make custom scales and assemble them on my own. The question is where does the small/medium batch line fall?

Other than that, stay tuned! I'm planning on attending the MIT Maker Faire on Oct 4th, so if you're around, feel free to drop by!

Doing More with Less

"I'm givin' her all she's got, Captain! If I push it any harder the whole thing will blow!"

Ok, oblique Star Trek reference aside, I managed to squeeze some more power out of the ATtiny84 chip that runs the Voltmeter Clock. Less oblique Star Trek reference, Mr. Sulu (George Takei) was in the Boston area this past week and I got to meet him! He was doing a video shoot for his youtube show and I happened to be in the right place at the right time!



Back to power reduction. Here were the key methods to get below 300uA:

• Getting to interrupt driven code last week was a big step, but with some reorganization, I made the interrupt service routines faster. I don't miss interrupts at the slower clock speed any more and overall, the chip spends more time in powered down mode. This got me under a 1mA.
  
• Changing the size of pull-up resistors. The ATtiny84 has internally selectable 70K ohm pullup resistors, while I was using 10K pullups in my previous version. I want to make the pullups that tie the encoder switch debounce filters high as large as possible, while still being able to drive the chip inputs.
  
• I sacrificed an output pin to enable / disable power to the potentiometer on the mode select knob. When the mode select knob isn't being polled, it is now completely disconnected. This and the last step got me to about 600uA.
  
• The last biggie was turning down the voltage. The chip was running at 5V power previously. The ATtiny84 also comes in a couple different flavors... the original, and also an 84V version and an 84A version that can run at even lower voltages. Turns out, I got lucky when I ordered breadboard parts and I had the 84A on hand. Turning the voltage down to 1.8V dropped the current draw all the way below 300uA.

Doing more with less

With some good data on hand, I can move forward with a little more confidence about board design. Two AA batteries in parallel should provide enough energy to last for more than a year, and Microchip Corp makes a switching regulator (I'm considering the MCP1624) designed specifically to provide a voltage boost to appropriate levels from a battery source.

The last big hurdle is "future proofing" the board layout. I'd love to have an alarm clock version of the clock, and if I can use the same printed circuit board for both products, but with different components, I'll be in much better shape.

Sacrificing an I/O pin earlier to power down the Mode Select Knob in between polling means having to work a teeny bit harder to add an "Alarm On/Off" switch. It's still possible to get clever and I try to read several switch states through one pin. If any EE's out there would like to critique the solution, I'd appreciate it.

• R2 is the "Mode Control" knob, SW1 is the optional "Alarm On/Off" switch
• AtoD conversion to the read the control knob switch / state is made at the "MODE SELECT" pin.
• Q1, Q2, R4, and SW1 may be unpopulated.
• The mode select knob should read between 0 - 1/2 Vcc with the switch open and from 1/2 - 1Vcc with the switch closed, giving distinct voltages for all states. With the unpopulated components, voltage will go from 1/3 - 2/3 Vcc.

What's Next?

The schematic is nearly done, then we'll be getting into board layout. This post has been heavy on the technical details and next week we'll get into more of the marketing tools / techniques we're using to manage our campaign.