Cheap and Effective Prototype Inventory Tracking

Design engineers understand the importance of inventory control. Finding the right system is a more difficult challenge.

At WrightGrid, where I work, we’ve developed a cheap, effective, and easy to use system for tracking our devices. As prototypes and development hardware moves from breadboard to production, we can see where we stand.

How? We put a unique ID number sticker on it.

To be clear, there’s a difference between what I call “prototype inventory control” and traditional production inventory control. I’m not trying to implement 6 sigma control of every last screw in the lab. I’m interested in tracking the higher level assemblies that engineers are working on. Especially as they carry the prototypes to their workbench, their desk, a test chamber, field tests, and so on and so forth. There’s a balance to strike between tracking inventory and, well, doing actual work.

The Wrong Way

I’d like to illustrate what happens without a system in place.

Pretend you have 3 populated circuit boards you’re doing work on. With the best of intentions, you say to yourself that you’ll keep track of them all. You start out knowing there is one on the workbench, one on your desk, and one in the box. This…is barely a plan. You will always move things, forget things, or someone else will move them without notifying you.

At the next level of sophistication, you’ll optimistically take a Sharpie and label your boards 1, 2, and 3. This is a slightly better plan. But invariably, you’ll have another revision of the boards, also marked with “1, 2, 3”. What then? When you’re looking through your notes, you’ll have no idea which #2 you’re referring to. We typically order 3–5 populated circuit boards per development cycle. We also average 2–3 cycles to get to a production ready design. That could be at least a dozen nearly identical boards floating around the lab! We need a better way.

The Cheap and Easy Way

At WrightGrid, we have a set of sequentially and uniquely numbered stickers that guarantees a unique “name” for every single item we deem worthy of tracking. We keep a running spreadsheet in Google Sheets and we write down the item number, the Dropbox folder with the original purchasing information (for us this implies revision as well), and any notes that we want to track. This could be things like the differences across boards, rework done on that board, or the last known location of the prototype. Simply apply the sticker, make a spreadsheet entry, and you’re good to go.

The use of the sticker system has become so ingrained into our company culture that it even has a sort of a mini ceremony around it:

“Let’s put a sticker on it!” means you’ve done something unique enough and important enough to be worthy of tracking.

We’ve spent a teeny bit more money to get nicer vinyl “asset tags” which are slightly more durable. This helps ensure they will survive environmental chambers and other regular wear-and-tear. But there’s no reason you couldn’t use inkjet printed mailer labels if you’d like to start implementing this system today. You could also go all out for heavy duty, permanent metallic foil labels.

I should add, even though we don’t use the bar codes and just use the human readable numbers, we added those to our stickers as well, because they look cool. We very easily could implement a scanner into our process later on.

Benefits of Use

Since developing this system, I’ve noticed about how the engineers have changed behaviors in response to this practice.

The engineers are now identifying boards by their ID number. This a permanent feature, rather than the board’s location (which is subject to change). They’ll say, “The #204, #205, and #206 boards need resistors swapped out. The #207 is on Alice’s desk.” They’re not saying “The three boards in the lab and the one being worked on.”

Sometimes generic “untracked” components come back from the field. These are not necessarily part of the final product assembly but we realize we’ll want to track the field returned unit for posterity. For example, we weren’t tracking individual batteries. To distinguish the battery with a field history, we simply applied a sticker when it came back in and put it into the database.

Testing documentation is now more in-depth than writing, “Circuit board batch Rev C,”. Now we write down “Circuit board #302 from batch Rev C.”

When new batches of parts come in, we tend to pull sticker numbers in blocks. Having unique ID’s avoids double counting inventory and the sequential block makes taking a total count easier as well.

Conclusion

Sophisticated inventory tracking systems do exist, but are not always required. In my experience, the large systems are too clumsy, slow, and difficult for engineers to use on a daily basis. Those should be used for their intended task,managing production inventory.

For tracking development work, a simple sticker and a spreadsheet have proven more than adequate for creating a fast, flexible, and reliable system that our engineers actually use.