AlexTheEngineer

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Long time no updates….

Uncategorized No Responses »

Aug 132016

There do seem to be folk who actually read this / stumble across the blog perhaps through searching for random tech stuff in spite of me rarely promoting it I thought I’d post an update and what I hope to do with this space..

Unfortunately last year I had to deal with a family bereavement as well as health problems/tiredness/burnout; often after I have finished with work-related tasks (which I try and prioritise my energy towards as I am lucky to have a very understanding and accomodating employer) I am way too tired for much else, such as music/creative stuff such as photography and tech/electronic projects.

Also slowly realising I am getting older and have had to make some different lifestyle choices; much less partying and late nights compared to my nearly two decades as a raver, DJ, party promoter etc. All good fun but starting to get a bit much in the end.

This has slightly reduced my enthusiasm for “harder” electronic music, so I have temporarily removed the online radiostation VFR Europe from here (as I hadn’t got the time to curate, upload and schedule content, let alone work on my home studio) although it will hopefully return in the future.

For those who want music there is still plenty on www.partyvibe.com

The good news is I am slowly regaining energy as well as getting into a better routine of sleep patterns, eating etc than in my “youth” (I still don’t consider myself to be old!) and there are still things I get up to I can blog about so hope to be posting here more often.

I don’t do “social networks” much – I (re)tweet occasionally at @vfrmedia (when I get round to it will add the twitter sidebar) and have no desire to become a “social media star” so this blog isn’t going to contain the latest “hip” technology; but will reflect my diverse tech/engineering interests (including “retro” stuff such as my reignited interest in fountain pens) as well as nature/and environment related content….

POCSAG pager transmitter using RF22 board and Arduino

Arduino, coding, radio 6 Responses »

Feb 062016

Since putting this project on Youtube I’ve had a surprising amount of interest from across the world about the modifications I made to the original code from ON1ARF ( a radioamateur in België) to allow 1200 and 2400 bps pager transmissions as well as the default 512bps (I wanted to use the circuit to test commercial POCSAG pager receivers used at one site at my work).

The original code is here

https://github.com/on1arf/pocsag

To get 1200 and 2400 bps you must alter the radiohead libraries it depends on.

Two files must change – the first is RH_RF22.cpp. The code snippet is below (cut and paste this into your editor)


					header file for Arduino POCSAG RF22 tx


			
			// These are indexed by the values of ModemConfigChoice
// Canned modem configurations generated with
// http://www.hoperf.com/upload/rf/RH_RF22B%2023B%2031B%2042B%2043B%20Register%20Settings_RevB1-v5.xls
// Stored in flash (program) memory to save SRAM
PROGMEM static const RH_RF22::ModemConfig MODEM_CONFIG_TABLE[] =
{
    { 0x2b, 0x03, 0xf4, 0x20, 0x41, 0x89, 0x00, 0x36, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x10, 0x62, 0x2c, 0x00, 0x08 }, // Unmodulated carrier
    { 0x2b, 0x03, 0xf4, 0x20, 0x41, 0x89, 0x00, 0x36, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x10, 0x62, 0x2c, 0x33, 0x08 }, // FSK, PN9 random modulation, 2, 5

    // All the following enable FIFO with reg 71
    //  1c,   1f,   20,   21,   22,   23,   24,   25,   2c,   2d,   2e,   58,   69,   6e,   6f,   70,   71,   72
    // FSK, No Manchester, Max Rb err <1%, Xtal Tol 20ppm
    { 0x2b, 0x03, 0xf4, 0x20, 0x41, 0x89, 0x00, 0x36, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x10, 0x62, 0x2c, 0x22, 0x08 }, // 2, 5
    { 0x1b, 0x03, 0x41, 0x60, 0x27, 0x52, 0x00, 0x07, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x13, 0xa9, 0x2c, 0x22, 0x3a }, // 2.4, 36
    { 0x1d, 0x03, 0xa1, 0x20, 0x4e, 0xa5, 0x00, 0x13, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x27, 0x52, 0x2c, 0x22, 0x48 }, // 4.8, 45
    { 0x1e, 0x03, 0xd0, 0x00, 0x9d, 0x49, 0x00, 0x45, 0x40, 0x0a, 0x20, 0x80, 0x60, 0x4e, 0xa5, 0x2c, 0x22, 0x48 }, // 9.6, 45
    { 0x2b, 0x03, 0x34, 0x02, 0x75, 0x25, 0x07, 0xff, 0x40, 0x0a, 0x1b, 0x80, 0x60, 0x9d, 0x49, 0x2c, 0x22, 0x0f }, // 19.2, 9.6
    { 0x02, 0x03, 0x68, 0x01, 0x3a, 0x93, 0x04, 0xd5, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x09, 0xd5, 0x0c, 0x22, 0x1f }, // 38.4, 19.6
    { 0x06, 0x03, 0x45, 0x01, 0xd7, 0xdc, 0x07, 0x6e, 0x40, 0x0a, 0x2d, 0x80, 0x60, 0x0e, 0xbf, 0x0c, 0x22, 0x2e }, // 57.6. 28.8
    { 0x8a, 0x03, 0x60, 0x01, 0x55, 0x55, 0x02, 0xad, 0x40, 0x0a, 0x50, 0x80, 0x60, 0x20, 0x00, 0x0c, 0x22, 0xc8 }, // 125, 125

    // { 0x2b, 0x03, 0xa1, 0xe0, 0x10, 0xc7, 0x00, 0x09, 0x40, 0x0a, 0x1d,  0x80, 0x60, 0x04, 0x32, 0x2c, 0x22, 0x04 }, // 512 baud, FSK, 2.5 Khz fd for POCSAG compatibility
    { 0x27, 0x03, 0xa1, 0xe0, 0x10, 0xc7, 0x00, 0x06, 0x40, 0x0a, 0x1d,  0x80, 0x60, 0x09, 0xd5, 0x2c, 0x22, 0x07 }, // 1200 baud, FSK, 4.5 Khz fd for POCSAG compatibility
    // { 0x27, 0x03, 0xa1, 0xe0, 0x10, 0xc7, 0x00, 0x06, 0x40, 0x0a, 0x1d,  0x80, 0x60, 0x04, 0x32, 0x2c, 0x22, 0x07 }, // 512 baud, FSK, 4.5 Khz fd for POCSAG compatibility
    // 2400 bps
    { 0x27, 0x03, 0xa1, 0xe0, 0x10, 0xc7, 0x00, 0x06, 0x40, 0x0a, 0x1d,  0x80, 0x60, 0x13, 0xa9, 0x2c, 0x22, 0x07 },// 2400 baud, FSK, 4.5 Khz fd for POCSAG compatibility
    
    // GFSK, No Manchester, Max Rb err <1%, Xtal Tol 20ppm
    // These differ from FSK only in register 71, for the modulation type
    { 0x2b, 0x03, 0xf4, 0x20, 0x41, 0x89, 0x00, 0x36, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x10, 0x62, 0x2c, 0x23, 0x08 }, // 2, 5
    { 0x1b, 0x03, 0x41, 0x60, 0x27, 0x52, 0x00, 0x07, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x13, 0xa9, 0x2c, 0x23, 0x3a }, // 2.4, 36
    { 0x1d, 0x03, 0xa1, 0x20, 0x4e, 0xa5, 0x00, 0x13, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x27, 0x52, 0x2c, 0x23, 0x48 }, // 4.8, 45
    { 0x1e, 0x03, 0xd0, 0x00, 0x9d, 0x49, 0x00, 0x45, 0x40, 0x0a, 0x20, 0x80, 0x60, 0x4e, 0xa5, 0x2c, 0x23, 0x48 }, // 9.6, 45
    { 0x2b, 0x03, 0x34, 0x02, 0x75, 0x25, 0x07, 0xff, 0x40, 0x0a, 0x1b, 0x80, 0x60, 0x9d, 0x49, 0x2c, 0x23, 0x0f }, // 19.2, 9.6
    { 0x02, 0x03, 0x68, 0x01, 0x3a, 0x93, 0x04, 0xd5, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x09, 0xd5, 0x0c, 0x23, 0x1f }, // 38.4, 19.6
    { 0x06, 0x03, 0x45, 0x01, 0xd7, 0xdc, 0x07, 0x6e, 0x40, 0x0a, 0x2d, 0x80, 0x60, 0x0e, 0xbf, 0x0c, 0x23, 0x2e }, // 57.6. 28.8
    { 0x8a, 0x03, 0x60, 0x01, 0x55, 0x55, 0x02, 0xad, 0x40, 0x0a, 0x50, 0x80, 0x60, 0x20, 0x00, 0x0c, 0x23, 0xc8 }, // 125, 125

    // OOK, No Manchester, Max Rb err <1%, Xtal Tol 20ppm
    { 0x51, 0x03, 0x68, 0x00, 0x3a, 0x93, 0x01, 0x3d, 0x2c, 0x11, 0x28, 0x80, 0x60, 0x09, 0xd5, 0x2c, 0x21, 0x08 }, // 1.2, 75
    { 0xc8, 0x03, 0x39, 0x20, 0x68, 0xdc, 0x00, 0x6b, 0x2a, 0x08, 0x2a, 0x80, 0x60, 0x13, 0xa9, 0x2c, 0x21, 0x08 }, // 2.4, 335
    { 0xc8, 0x03, 0x9c, 0x00, 0xd1, 0xb7, 0x00, 0xd4, 0x29, 0x04, 0x29, 0x80, 0x60, 0x27, 0x52, 0x2c, 0x21, 0x08 }, // 4.8, 335
    { 0xb8, 0x03, 0x9c, 0x00, 0xd1, 0xb7, 0x00, 0xd4, 0x28, 0x82, 0x29, 0x80, 0x60, 0x4e, 0xa5, 0x2c, 0x21, 0x08 }, // 9.6, 335
    { 0xa8, 0x03, 0x9c, 0x00, 0xd1, 0xb7, 0x00, 0xd4, 0x28, 0x41, 0x29, 0x80, 0x60, 0x9d, 0x49, 0x2c, 0x21, 0x08 }, // 19.2, 335
    { 0x98, 0x03, 0x9c, 0x00, 0xd1, 0xb7, 0x00, 0xd4, 0x28, 0x20, 0x29, 0x80, 0x60, 0x09, 0xd5, 0x0c, 0x21, 0x08 }, // 38.4, 335
    { 0x98, 0x03, 0x96, 0x00, 0xda, 0x74, 0x00, 0xdc, 0x28, 0x1f, 0x29, 0x80, 0x60, 0x0a, 0x3d, 0x0c, 0x21, 0x08 }, // 40, 335
};
		
				
					RH_RF22.cpp
					view raw

Also the header file RH_RF22.h must change so the modemconfig table has values that reflect the changed modulation schemes.

RF22 headerfile

typedef enum { UnmodulatedCarrier = 0, ///< Unmodulated carrier for testing FSK_PN9_Rb2Fd5, ///< FSK, No Manchester, Rb = 2kbs, Fd = 5kHz, PN9 random modulation for testing FSK_Rb2Fd5, ///< FSK, No Manchester, Rb = 2kbs, Fd = 5kHz FSK_Rb2_4Fd36, ///< FSK, No Manchester, Rb = 2.4kbs, Fd = 36kHz FSK_Rb4_8Fd45, ///< FSK, No Manchester, Rb = 4.8kbs, Fd = 45kHz FSK_Rb9_6Fd45, ///< FSK, No Manchester, Rb = 9.6kbs, Fd = 45kHz FSK_Rb19_2Fd9_6, ///< FSK, No Manchester, Rb = 19.2kbs, Fd = 9.6kHz FSK_Rb38_4Fd19_6, ///< FSK, No Manchester, Rb = 38.4kbs, Fd = 19.6kHz FSK_Rb57_6Fd28_8, ///< FSK, No Manchester, Rb = 57.6kbs, Fd = 28.8kHz FSK_Rb125Fd125, ///< FSK, No Manchester, Rb = 125kbs, Fd = 125kHz FSK_Rb_1200Fd4_5, ///< FSK, No Manchester, Rb = 1200bs, Fd = 4.5kHz, for POCSAG compatibility // FSK_Rb_512Fd4_5, ///< FSK, No Manchester, Rb = 512bs, Fd = 4.5kHz, for POCSAG compatibility FSK_Rb_2400Fd4_5, ///< FSK, No Manchester, Rb = 2400bs, Fd = 4.5kHz, for POCSAG compatibility GFSK_Rb2Fd5, ///< GFSK, No Manchester, Rb = 2kbs, Fd = 5kHz GFSK_Rb2_4Fd36, ///< GFSK, No Manchester, Rb = 2.4kbs, Fd = 36kHz GFSK_Rb4_8Fd45, ///< GFSK, No Manchester, Rb = 4.8kbs, Fd = 45kHz GFSK_Rb9_6Fd45, ///< GFSK, No Manchester, Rb = 9.6kbs, Fd = 45kHz GFSK_Rb19_2Fd9_6, ///< GFSK, No Manchester, Rb = 19.2kbs, Fd = 9.6kHz GFSK_Rb38_4Fd19_6, ///< GFSK, No Manchester, Rb = 38.4kbs, Fd = 19.6kHz GFSK_Rb57_6Fd28_8, ///< GFSK, No Manchester, Rb = 57.6kbs, Fd = 28.8kHz GFSK_Rb125Fd125, ///< GFSK, No Manchester, Rb = 125kbs, Fd = 125kHz OOK_Rb1_2Bw75, ///< OOK, No Manchester, Rb = 1.2kbs, Rx Bandwidth = 75kHz OOK_Rb2_4Bw335, ///< OOK, No Manchester, Rb = 2.4kbs, Rx Bandwidth = 335kHz OOK_Rb4_8Bw335, ///< OOK, No Manchester, Rb = 4.8kbs, Rx Bandwidth = 335kHz OOK_Rb9_6Bw335, ///< OOK, No Manchester, Rb = 9.6kbs, Rx Bandwidth = 335kHz OOK_Rb19_2Bw335, ///< OOK, No Manchester, Rb = 19.2kbs, Rx Bandwidth = 335kHz OOK_Rb38_4Bw335, ///< OOK, No Manchester, Rb = 38.4kbs, Rx Bandwidth = 335kHz OOK_Rb40Bw335 ///< OOK, No Manchester, Rb = 40kbs, Rx Bandwidth = 335kHz } ModemConfigChoice;

RH_RF22.h

view raw

the rest can then be used as normal – remember to alter the main Arduino sketch code to select these new bps rates.

NB: I am based in the UK/Europe; we always use wide deviation for POCSAG signals (although much other PMR traffic is now on narrow deviation).

If your country’s Communications Ministry requires narrow deviation to be used you will have to recalculate the modem settings using the spreadsheet referred to in the library files. (Its not as bad as it might seem; I had to use it to get the 1200/2400bps settings and I am not an RF nor a coding expert by any means)

soundprocessing on 100V PA amplifier /.LS system

Uncategorized No Responses »

Sep 072015

Deprecated: Function get_magic_quotes_gpc() is deprecated in /homepages/42/d24067567/htdocs/clickandbuilds/WordPress/rtn_vfrmedia_newblog/wp-includes/formatting.php on line 4798

I used the Japanese Multimax program + two obsolete XP PC’s. The PC also has a second soundcard connected to Ekiga on auto answer so dialling extension 338 will allow announcements to be made on the PA amp (it is connected to an input with auto vox volume ducking).

Chinese PABX instructions

ratsaladpark, telecommunications / telecommunicatie No Responses »

Aug 192015

This PABX is now sold as an improved version with a better translated manual; but (as I have some Chinese ancestry on my fathers side) I prefer the “Chinglish” version 😀

and some ARM assembler….

coding, raspberry pi No Responses »

Aug 082015

gcc can compile either c source or assembler (.s extension) or even a combination of both.

As I had the assembler source, decided to experiment with altering the string data (I don’t yet know enough to do anything else).

it still worked 🙂

note how the addresses of the array pointer change, as the strings have grown by a few characters…

below is the original code

of course this is basic easy stuff; those strings are static/constant data and declared at compile time. if your code is dealing with strings that can change their length, it must always have sufficient free memory allocated to wherever the string data ends up, enough for the largest of the data. Otherwise you get a buffer overflow and your goose is cooked…