This page is a work in progress and will be updated on the way.
Last update: 2015-03-04
| Part | Comment | Cost | Am | Source |
|---|---|---|---|---|
| Realtek RTL2832U | Radio receiver | 12-23 € | 1 | Amazon(DE) Ebay NooElec(US) |
| LM2596 Board | Voltage regulator | 2-6 € | 1 | Ebay(HK) |
| Arduino Micro Pro | Microcontroller | 12-20€ | 1 | Amazon(DE) Sparkfun(US) |
| TP-Link WR703N | Router | 25€ | 1 | Ebay |
| Pololu A49888 | Stepper motor driver | 5€ | 2 | Pololu(US) Ebay |
| NEMA 17 | Stepper motor | 15€ | 2 | Pololu(US) Ebay Stepperonline |
| Sum | 91-114€ |
The prices included are the prices I found for which you can buy these components new. Many of those parts are well known in the hacking world and you often find them overpriced, therefore you can take these prices as an orientation.
RTLSdr (RTL2832)
The software defined radio USB stick is basically just a hacked DVB stick. You can find those at cheap prices starting from 12 €uro everywhere. However, since this products is not intended for this purpose, some improvements can be made to the design, for instance a better crystal oscillator for better frequency stability or diodes for a smoother supply voltage. This improvements can have effect on your temperature stability and frequency offset. However those are not critical, but a nice feature to have for just a couple Euro more.
Further, the receiver comes with a variety of different (supported) tuners (E4000, R820T, R820T2 among those as the ones which are most commonly around).
The E4000 was the original tuner which is said to have better performance than the later R820T. However ever since the E4000 is now hardly available and prices have skyrocketed. Between the R820T and R820T2 a comparison shows a marginally better background noise and sensitivity is achieved by the R820T2.
LM2596 Voltage regulator
The LM2596 is a very small, however very powerful and efficient switching step-down voltage regulator. It creates a lower output voltage (as for instance 5V) from a higher supply voltage. They can supply up to 2-3 amps which is sufficient for most projects and have a very small footprint. To avoid designing the whole converter including inductors, capacitors etc. you can buy simple breakout boards for just several €uro. However be aware that there exist plenty different breakout boards of different sizes. Use the ones which have dimensions of about 41mmx21mm, e.g. the common small footprint without a voltage display.
The breakout boards you commonly find only have an 33μH as you can see on the pictures (inductor marking 330). According to the datasheet the inductance for 12V->5V would be best to have a higher inductance (68 μH), but for the currents required, less than 1 Ampere@5 Volts, is still highly sufficient. The 5 Volt line has to supply has to power the RTLSDR takes about ~300mA, WR703N router about ~100mA, the Arduino usually at less than ~25mA.
TP-LINK WR703N
Although you could use any (old) router that supports the open-source firmware OpenWRT that has USB, the WR703N advantages are its very small size (57x57x18mm³), very low power consumption and price, and that it is well known to the OpenWRT community (which is worth a lot). Disadvantages generally speaking are the fact that it has no external Wifi antenna and in the lower range of ram and flash memory. (Although there are documented hacks to increase both). If you are willing to invest some Euro more you can probably go for other supported routers (e.g. tl-wr1043nd) but then you can quickly run into space problems inside the tracking box.
Be sure not to buy the WR702N, although very similar it has to few memory to run the linux distribution and is therefore absolutely unusable for this purpose.
You can get this one for instance on Ebay or Amazon for less than 25€.
