Part Selection
After the overview and specifications of your board, the parts used in the design must be selected. Nearly all parts can be picked from a few distributer websites, but some parts are only available through the manufacturer. Be sure to check multiple locations to get the best part.
1. Digi-key
2. Mouser
3. Newark
Check out each of these sites and browse around. It is easiest to order all the parts from a single distributer, but it is not required. Also, if you are using a chip you are unfamiliar with, try to get free samples from the manufacturer. For example, Texas Instruments (TI) is very good about offering free samples of chips for first time users. To select the proper chips, you should create a cost-benefit matrix and compare each of the specifications for the chip.
GPS Selection Example
Let's investigate an example of selecting a GPS chip to use in a hardware design. For this design, the device will be used for long trips with limited battery power and used to collect the data every few minutes. With limited battery power, the low power properties of the chips become a major design consideration. The characteristics of the chips can be found on the various data sheets and are summarized in the table below.
1. Digi-key
2. Mouser
3. Newark
Check out each of these sites and browse around. It is easiest to order all the parts from a single distributer, but it is not required. Also, if you are using a chip you are unfamiliar with, try to get free samples from the manufacturer. For example, Texas Instruments (TI) is very good about offering free samples of chips for first time users. To select the proper chips, you should create a cost-benefit matrix and compare each of the specifications for the chip.
GPS Selection Example
Let's investigate an example of selecting a GPS chip to use in a hardware design. For this design, the device will be used for long trips with limited battery power and used to collect the data every few minutes. With limited battery power, the low power properties of the chips become a major design consideration. The characteristics of the chips can be found on the various data sheets and are summarized in the table below.
Chip | Manufacturer | Time to Acquire (s) | Searching Current (mA) | Energy To Acquire (J) | Tracking Sens. (dBm) | DC Supply (V) | Channels | Operating Temp. (C) | Cost |
---|---|---|---|---|---|---|---|---|---|
MAX-7C | u-blox | 29 | 17.5 @ 3.3 V | 1.5 | -161 | 1.65 to 3.6 | 56 | -40 to 85 | 79.00 |
Venus 638 D | SkyTraq | 29 | 18 @ 3.3 V | 1.7 | -165 | 2.8 to 3.6 | 65 | -40 to 85 | 40.00 |
RXM-GPS-RM-B | Linx | 32 | 14 @ 3.3 V | 1.5 | -161 | 3.0 to 4.3 | 66 | -40 to 85 | 19.34 |
When selecting a chip, it is imperative to decide what is the most important characteristic for your application. If the GPS is going to be used at low elevations, the high tracking sensitivity may be the most important, so the Venus chip should be used with an active antenna. For this example's applications, low acquisition energy is the key characteristic, therefore the u-blox or Linx chip can be used. Since the Linx chip is widely available on Mouser and has a lower price than the u-blox chip, the Linx chip should be chosen for the design.
For each chip on your board, there should be an analysis table similar to the one on GPS chips above. In addition to being helpful for the designer, it is ideal to explain to others why a certain chip has been selected. After chip selection, try using www.octopart.com to view where the parts can be bought and how much they cost.
For each chip on your board, there should be an analysis table similar to the one on GPS chips above. In addition to being helpful for the designer, it is ideal to explain to others why a certain chip has been selected. After chip selection, try using www.octopart.com to view where the parts can be bought and how much they cost.