Sensor Board Programming

Tuning the Bluetooth Radio

Each BlueCore3 baseband is self calibrated according to the ambient/chip temperature and the input clock. Since the chip takes care of tuning the temperature we just need to set the appropriate tweaking for the crystal, this is set by:

• the BlueCore radio broadcast an RF signal at what it believes 2.441GHz
• a spectrum analyzer set to 2.441GHz scanning the RF spectrum for this signal
• a crystal trim value that adjusts the BlueCore's signal until it outputs a true 2.441Ghz signal

The basic process is:

1. Program the firmware and persistent store keys on the Bluetooth radio
2. Determine the crystal trim value (in hexadecimal) using a spectrum analyzer
3. Convert the hexadecimal number to decimal
4. Program the converted value into the persistent store keys

Setting up the Spectrum Analyzer

Any 2.4GHz spectrum analyzer will work the only requirement is it being somewhat calibrated and having an appropriate 2.4GHz antenna. The instructions below are for using a Tekntronix RSA3408A 8GHz digital spectrum analyzer. Here are the steps to setup the spectrum analyzer so you can tune the radio:

1. With the spectrum analyzer off, plug in the 2.4GHz antenna.
   • This should require no force and doesn’t have to be very tight, be careful to not bend or break any of the delicate leads
2. Turn on the spectrum analyzer it will boot into Window sXP and after a few moments will start the spectrum analyzer software.
   • It is generally a good idea to leave the system running for about 15minutes before you use it so the device has a chance to warm up and calibrate itself.
3. First we set the center frequency, by hitting button 3
4. Enter "2.441" on the keypad
5. Hit the "GHz" button to indicate that its 2.441GHz
6. Next we set the span (how wide the visible spectrum is) by hitting button 6
7. Then we enter "400" on the keyboard
8. And hit the "kHz" button to indicate a span of 400kHz, in general all the Bluetooth radios should transmit within this span but you can set it lower or higher if needed
9. Once the radio is transmitting there should be a single peak like the one shown in the figure. By default the purple cursor (seen as a small box on the right side of the peak in the picture) will point to our desired center frequency of 2.441GHz. If you want you can hit the "peak" button to have the cursor highlight what frequency the highest peak is at. In general its better to leave the cursor at 2.441GHz so you don't end up using the wrong center frequency by mistake. You can reset the cursor by entering 2.441GHz in the keypad.

The CFG XTAL FTRIM value is set in hexadecimal, however, the "Crystal Frequency Trim" value is set in decimal. Here's a quick look up table for mapping from hexadecimal to decimal:

Hexadecimal	Decimal	Hexadecimal	Decimal	Hexadecimal	Decimal
0x10	16	0x20	32	0x30	48
0x11	17	0x21	33	0x31	49
0x12	18	0x22	34	0x32	50
0x13	19	0x23	35	0x33	51
0x14	20	0x24	36	0x34	52
0x15	21	0x25	37	0x35	53
0x16	22	0x26	38	0x36	54
0x17	23	0x27	39	0x37	55
0x18	24	0x28	40	0x38	56
0x19	25	0x29	41	0x39	57
0x1A	26	0x2A	42	0x3A	58
0x1B	27	0x2B	43	0x3B	59
0x1C	28	0x2C	44	0x3C	60
0x1D	29	0x2D	45	0x3D	61
0x1E	30	0x2E	46	0x3E	62
0x1F	31	0x2F	47	0x3F	63