The Design Process Getting Output From Your System by Prof. Michalson

Design Problem We’ve been working on a system that receives input, performs some kind of processing, and produces an output display. The display should must provide a 3 digit number indicating, for example, water (fluid) temperature.

A System Block Diagram Analog Input Processing Power Supply Display Micro controller

A Really Simple Display Lots of displays are: –1) LEDs –2) Based on collections of LEDs –3) Have similarities to displays made with LEDs So, let’s see what’s involved with using just an LED. –It won’t meet our requirements, but we need to gain expertise first, then apply that new knowledge to achieve what we want.

Turning On an LED To light an LED generally requires: –Forward biasing the LED –Controlling the current through the LED How can we know: –What’s important? –What “typical” means? –What the details of lighting an LED are? Course textbooks Other (Google “Using LEDs”)

We Quickly Find Direction! A little searching and we find lots of information about LEDs Including a circuit! Source: Using LEDs – It’s Easy, Jaycar Electronics

Refining Our System Design Based on our searching, we’ve learned some things that are important to look for when selecting an LED. Specifically, we need to consider: –LED color –Forward Current (I F ) –Forward voltage (V LED ) In our system we also need to consider: –Supply voltage/current

Datasheets?!?!? Our research also helps us select components. For example, go to digikey.com There are many, many options! –Sorting options may require more research! Let’s try: –Green –50 mcd (typical indicator light) –Maximum viewing angle

HSME-C265-ND Datasheet The first thing I notice on the datasheet is a picture of the device! It’s not very convenient for our project! However, it’s not totally useless, since it at least lets us see the typical information that’s provided.

Back to the Drawing Board! We now know that package styles are important! Let’s focus our search a little more: –Package style –Color –Brightness –Etc. We finally find a (potentially) suitable component!

But We Need a 3-Digit Display! We basically know how to drive an LED. A multi-digit display is really a bunch of LEDs in a single package. We can repeat the process we just used to try to find a suitable 3-digit display. Consider the following Digi-Key parts: – ND – ND

But Wait, There’s More… Now we have some ideas how to: –Drive an LED –Interpret a datasheet –Find (potentially) suitable components Next, we need to see how the options we find for actual output devices impact the circuitry that actually drives the display.

Ramifications… Hardware-related considerations: –Processor drive capabilities VoltageCurrent –Pin counts Drive each pin separately or multiplex lines? Software-related considerations: –Encoding of data to drive display –Scan rate of display –Etc.

Design = Iteration? Every decision you make at one point in a design will impact decisions made at another point in the design. Thus, every decision may require revisiting previous decisions. Sometimes you’ll find that things won’t work together the way you planned. –It’s better to find out before you start building! Iterate through design options until all your requirements are satisfied.