The ability to reuse existing sections of designs is like the quest for the holy grail in our design team - something we value highly and dream of finding, but have yet to discover. And if you were to push me to take a position, I used to doubt it would ever be found.

So I'd have to say that I was skeptical when I read statements about design reuse in Altium Designer - "I'll believe that when I see it" were my exact words.

Everyone in the team was already practicing design re-use, we were copying and pasting sections of existing designs " like standard comms or power supply sub-circuits " into our current projects.

But there was no integrity in the copied design, because any number of mistakes could be made during the copy/paste process, and the engineer could and would modify the circuit to suit their idea of a good circuit. That meant it had to be subject to the standard review and triple-check sign-off process.

The challenges of design reuse
For design reuse to work, there are a couple of fundamental challenges that must be solved.

1. The schematics must be available for everyone to use, but secure from any editing. We want everyone in the team to be able to easily explore and use all our proven circuits, with all additions and changes controlled and managed by our formal review process.

2. Since this central resource cannot be edited, the design environment must support the ability to update the component designators on each new design. This must be done without affecting the assignments on the master copy (as that would break rule 1). This has always been the deal-breaker in the past " how to maintain unique component designations in the new design, without resorting to some complex and convoluted naming scheme, like R1_Power_1v2, in the master re-use copy.

Well, it's time for this skeptic to put his money where his mouth is. My current design has been prototyped on the Desktop NanoBoard, and it's time to move it to a custom board. I can save loads of time and accelerate that process if I re-use circuitry directly from the Desktop NanoBoard, so it's time to brave the waters of design reuse.

An elegant approach to design reuse
Like any engineer, I'm always curious to see how things work. So when my snazzy new NanoBoard arrived I had the schematic and board files open in Altium Designer as soon as the board itself had been plugged in and powered up.

One of the first things that caught my eye on the top schematic sheet for the NB2 was the recycling symbol inside some of the sheet symbols, ahown below:

Pressing F1 (see in Figure 1 below) as I hovered the mouse over the symbol, I discovered that this was a Device Sheet Symbol (instead of a standard sheet symbol), which points to a Device Sheet, and that Device Sheets are reusable blocks of circuitry.

Figure 1. Altium Device Sheet Menu

I now knew that a reusable chunk of circuitry was called a Device Sheet, and it was accessed by placing a Device Sheet Symbol. And by clicking the link in the summary in the Knowledge Center panel, I had a PDF called Using Device Sheets open, ready to guide me.

I drilled down into one of the Device Sheets on the NanoBoard schematic, the USB in fact, because my design would use the same USB device (Figure 2, below). The Device Sheet had interesting watermarks on it, the recycling symbol was there again, and also the text, Read Only. I printed the sheet to check that the watermarks were not included, but just the circuitry printed as I'd hoped. They were useful on-screen, but I definitely did not want them included in the client's PDF!

Figure 2. Device Sheets are standard schematics, but because they are placed as a Device Sheet Altium Designer can be configured to show them as read only, and recycled.

(To  view a larged view of this figure, click here.)

I then checked the help PDF to learn more. I was happy to read that a Device Sheet is actually just a standard schematic sheet, which means it will be straightforward to take sheets from our existing designs and reuse them as Device Sheets.

I also learned that while a Device Sheet lets me reuse a chunk of circuitry, I could also build a hierarchy of Device Sheets if needed. This is perfect for those situations where there is a larger section to be reused.