Topic: Raw Temperature Data from Davis ISS Not Behaving as Dekay Describes

[KevDev]

Thanks to everyone's previous work, I am receiving data packets from the Davis ISS using a Raspberry Pi, Node.js, and an AdaFruit RFM69 radio.

The problem is with the temperature (message 8 ).  I have two Davis stations, one of them sends the temperature in the way Dekay describes (simply divide the received value by 160 to get the degrees F).  The other station sends it in a format that I cannot decode.  STRMON matches what I am receiving so I know the data is correct.  The console displays the correct real temperatures from this format so it knows how to decode it.

The station that works as Dekay describes was purchased in 2009; the one with the strange values was purchased about 2004.

Here are a few samples to show the mystery message 8 values - the columns are hop index, packet bytes, freq, signal strength, millis since last packet, temperature bytes and console temp (x10 so 181 = 18.1F).  As you can see the rcvd value decreases as the actual temp increases - specifically, the received value decreases by 0x40 for each 0.1 degree increase in actual temp (with a skip once in a while).

Has anyone seen this before?  I have plenty more samples that I can post if needed.

Thank you,
Kevin


 0 :  80 00 77 b5 c1 00 f7 12 ff ff -- 911413818 -72.0dBm -- 2606ms  rcvd: b5c1, console: 180
24 :  80 00 77 b5 81 00 fa de ff ff -- 909406860 -71.0dBm -- 2508ms  rcvd: b581, console: 181
48 :  80 00 77 b5 41 00 ec 8a ff ff -- 907901123 -66.0dBm -- 2605ms  rcvd: b541, console: 183
21 :  80 00 77 b5 01 00 e1 46 ff ff -- 903385376 -73.0dBm -- 2606ms  rcvd: b501, console: 184
 2 :  80 00 77 b4 c1 00 c0 22 ff ff -- 911915161 -74.0dBm -- 2604ms  rcvd: b4c1, console: 186
30 :  80 00 77 b4 81 00 cd ee ff ff -- 902884521 -70.5dBm -- 2508ms  rcvd: b481, console: 188
 7 :  80 00 77 b4 41 00 db ba ff ff -- 918438354 -70.0dBm -- 2503ms  rcvd: b441, console: 189
31 :  80 00 77 b4 01 00 d6 76 ff ff -- 910912109 -67.0dBm -- 2605ms  rcvd: b401, console: 191
 8 :  80 00 77 b3 c1 00 45 b2 ff ff -- 908904663 -74.0dBm -- 2604ms  rcvd: b3c1, console: 192
32 :  80 00 77 b3 81 00 48 7e ff ff -- 921949707 -72.5dBm -- 2504ms  rcvd: b381, console: 194
 9 :  80 00 77 b3 41 00 5e 2a ff ff -- 920445374 -74.5dBm -- 2508ms  rcvd: b341, console: 195
41 :  80 00 77 b3 01 00 53 e6 ff ff -- 904389343 -69.5dBm -- 2612ms  rcvd: b301, console: 197
18 :  80 00 77 b2 c1 00 72 82 ff ff -- 907399414 -66.5dBm -- 2503ms  rcvd: b2c1, console: 199
46 :  80 00 77 b2 81 00 7f 4e ff ff -- 905391968 -69.0dBm -- 2504ms  rcvd: b281, console: 200
23 :  80 00 77 b2 41 00 69 1a ff ff -- 923456299 -78.0dBm -- 2604ms  rcvd: b241, console: 202
 4 :  80 00 77 b2 01 00 64 d6 ff ff -- 914926575 -73.5dBm -- 2604ms  rcvd: b201, console: 203
36 :  80 00 77 b1 c1 00 2b d2 ff ff -- 927469849 -75.0dBm -- 2505ms  rcvd: b1c1, console: 205
17 :  80 00 77 b1 81 00 26 1e ff ff -- 921448364 -71.0dBm -- 2505ms  rcvd: b181, console: 206

[johnd]

I can't help with the decoding but it might be useful if you could identify the station that's misbehaving more exactly. Is the product number definitely 6152 or 6162 or 6163? (Or possibly 6312?)

VP2 stations were released only right at the end of 2004 IIRC. So, are you sure that this is a VP2 station and not eg a VP1? And, second, even if it is a VP2, the first generation VP2 stations had an analogue temp/hum sensor for a year or so, which might conceivably have affected the temperature encoding.

[KevDev]

The console says Vantage Pro2, Product # 6312, Model No. 6152.
The ISS says 6152.

[KevDev]

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[johnd]

OK, fair enough. Though with that Mfg Code it was one of the first production batches of VP2 stations IIRC. The comment about the analogue T/H still applies, though I'm not clear why that would make any difference to the wireless packets, but just remarking that it is a potentially notable difference from a station that DeKay might have used subsequently.

Edit: Just to provide a bit more detail for anyone unfamiliar: That's a Nov 2004 station. From later in 2005 (Oct?) the ISS firmware was changed to (from memory) v1.6, which was shown in a little circular label on top of one of the SIM board chips. The v1.6 F/W was also compatible with the SHT11 digital T/H chips that started to be used about the same time. Of course, this could be a complete red herring, but I'm guessing that it might be relevant.

[KevDev]

Thanks for your help johnd.

... with that Mfg Code it was one of the first production batches of VP2 stations IIRC.
[snip]
it is a potentially notable difference from a station that DeKay might have used subsequently.

That figures  .

Well, if anyone wants to take a stab at trying to decipher it, I'd very much appreciate the help.  I've tried lots of things like taking the 2's compliment of the received value and shifting it to the right to get the LSB to increment one with each 1/10 degree increment in the real value. 

Would it be considered bad forum etiquette to post a hundred lines or so of values over a broader temperature range to help those wanting to have a go at it?

[davidefa]

I'd say equation is as follow ( numbers are in hex ):

T = (0xD28E-rcvd)*0x19/0x400

Certainly figures are a bit strange

[KevDev]

I'd say equation is as follow ( numbers are in hex ):

T = (0xD28E-rcvd)*0x19/0x400

Certainly figures are a bit strange

Well that is close given what you had to work with.  The offset is not linear over a temperature range.

Here is sampling of data over a wider temperature range:


26 :  80 00 77 b7 c1 00 99 72 ff ff -- 905894592 -74.0dBm -- 2609ms  rcvd: b7c1, console: 167
20 :  80 00 77 b7 01 00 8f 26 ff ff -- 912919067 -67.0dBm -- 2604ms  rcvd: b701, console: 172
46 :  80 00 77 b6 41 00 b5 da ff ff -- 905391968 -69.0dBm -- 2507ms  rcvd: b641, console: 177
24 :  80 00 77 b5 81 00 fa de ff ff -- 909406860 -71.0dBm -- 2508ms  rcvd: b581, console: 181
 2 :  80 00 77 b4 c1 00 c0 22 ff ff -- 911915161 -74.0dBm -- 2604ms  rcvd: b4c1, console: 186
31 :  80 00 77 b4 01 00 d6 76 ff ff -- 910912109 -67.0dBm -- 2605ms  rcvd: b401, console: 191
 9 :  80 00 77 b3 41 00 5e 2a ff ff -- 920445374 -74.5dBm -- 2508ms  rcvd: b341, console: 195
46 :  80 00 77 b2 81 00 7f 4e ff ff -- 905391968 -69.0dBm -- 2504ms  rcvd: b281, console: 200
36 :  80 00 77 b1 c1 00 2b d2 ff ff -- 927469849 -75.0dBm -- 2505ms  rcvd: b1c1, console: 205
26 :  80 00 77 b1 01 00 3d 86 ff ff -- 905894592 -72.0dBm -- 2608ms  rcvd: b101, console: 210
16 :  80 00 77 b0 41 00 07 7a ff ff -- 915929138 -68.0dBm -- 2510ms  rcvd: b041, console: 214
33 :  80 00 77 af 81 00 7e 7c ff ff -- 915427856 -71.0dBm -- 2508ms  rcvd: af81, console: 219
 7 :  80 00 77 ae c1 00 44 80 ff ff -- 918438354 -69.5dBm -- 2600ms  rcvd: aec1, console: 224
20 :  80 00 77 ae 01 00 52 d4 ff ff -- 912919067 -72.0dBm -- 2505ms  rcvd: ae01, console: 229
33 :  80 00 77 ad 41 00 06 48 ff ff -- 915427856 -73.0dBm -- 2607ms  rcvd: ad41, console: 233
42 :  80 00 77 ac 81 00 27 2c ff ff -- 923957153 -76.0dBm -- 2608ms  rcvd: ac81, console: 238
31 :  80 00 77 ab c1 00 af 70 ff ff -- 910912109 -71.0dBm -- 2608ms  rcvd: abc1, console: 242
32 :  80 00 77 ab 01 00 b9 24 ff ff -- 921949707 -74.5dBm -- 2504ms  rcvd: ab01, console: 247
29 :  80 00 77 aa 41 00 83 d8 ff ff -- 924960205 -71.5dBm -- 2607ms  rcvd: aa41, console: 251
22 :  80 00 77 a9 81 00 cc dc ff ff -- 917434387 -81.0dBm -- 2607ms  rcvd: a981, console: 256
19 :  80 00 77 a8 c1 00 f6 20 ff ff -- 926967651 -79.5dBm -- 2501ms  rcvd: a8c1, console: 260
20 :  80 00 77 a8 01 00 e0 74 ff ff -- 912919067 -70.0dBm -- 2606ms  rcvd: a801, console: 264
17 :  80 00 77 a7 41 00 c1 89 ff ff -- 921448364 -72.0dBm -- 2503ms  rcvd: a741, console: 269
14 :  80 00 77 a6 81 00 e0 ed ff ff -- 910409912 -68.5dBm -- 2504ms  rcvd: a681, console: 273
 7 :  80 00 77 a5 c1 00 b4 71 ff ff -- 918438354 -72.0dBm -- 2606ms  rcvd: a5c1, console: 278
 0 :  80 00 77 a5 01 00 a2 25 ff ff -- 911413818 -80.5dBm -- 2603ms  rcvd: a501, console: 282
40 :  80 00 77 a4 41 00 98 d9 ff ff -- 918940125 -70.5dBm -- 2603ms  rcvd: a441, console: 287
29 :  80 00 77 a3 81 00 0b 1d ff ff -- 924960205 -70.5dBm -- 2509ms  rcvd: a381, console: 291
14 :  80 00 77 a2 c1 00 31 e1 ff ff -- 910409912 -71.0dBm -- 2606ms  rcvd: a2c1, console: 295
42 :  80 00 77 a2 01 00 27 b5 ff ff -- 923957153 -78.0dBm -- 2604ms  rcvd: a201, console: 298
31 :  80 00 77 a1 41 00 73 29 ff ff -- 910912109 -72.5dBm -- 2509ms  rcvd: a141, console: 304
16 :  80 00 77 a0 81 00 52 4d ff ff -- 915929138 -73.0dBm -- 2603ms  rcvd: a081, console: 309
 5 :  80 00 77 9f c1 00 b6 15 ff ff -- 906395874 -79.0dBm -- 2499ms  rcvd: 9fc1, console: 313
45 :  80 00 77 9f 01 00 a0 41 ff ff -- 919943604 -73.5dBm -- 5825ms  rcvd: 9f01, console: 318
34 :  80 00 77 9e 41 00 9a bd ff ff -- 906898071 -72.5dBm -- 2607ms  rcvd: 9e41, console: 322
23 :  80 00 77 9d 81 00 d5 b9 ff ff -- 923456299 -80.0dBm -- 2505ms  rcvd: 9d81, console: 327
12 :  80 00 77 9c c1 00 ef 45 ff ff -- 916933533 -79.5dBm -- 2510ms  rcvd: 9cc1, console: 331
 1 :  80 00 77 9c 01 00 f9 11 ff ff -- 902381897 -69.0dBm -- 2607ms  rcvd: 9c01, console: 335
41 :  80 00 77 9b 41 00 71 4d ff ff -- 904389343 -69.5dBm -- 2604ms  rcvd: 9b41, console: 340
34 :  80 00 77 9a 81 00 50 29 ff ff -- 906898071 -72.0dBm -- 2611ms  rcvd: 9a81, console: 344
19 :  80 00 77 99 c1 00 04 b5 ff ff -- 926967651 -73.5dBm -- 2509ms  rcvd: 99c1, console: 347
 8 :  80 00 77 99 01 00 12 e1 ff ff -- 908904663 -83.0dBm -- 2608ms  rcvd: 9901, console: 353
 1 :  80 00 77 98 41 00 28 1d ff ff -- 902381897 -70.5dBm -- 2604ms  rcvd: 9841, console: 358
45 :  80 00 77 97 81 00 12 78 ff ff -- 919943604 -71.0dBm -- 2605ms  rcvd: 9781, console: 362
38 :  80 00 77 96 c1 00 28 84 ff ff -- 908402893 -71.5dBm -- 2606ms  rcvd: 96c1, console: 366
35 :  80 00 77 96 01 00 3e d0 ff ff -- 917935669 -72.0dBm -- 2604ms  rcvd: 9601, console: 370
24 :  80 00 77 95 41 00 6a 4c ff ff -- 909406860 -78.0dBm -- 2602ms  rcvd: 9541, console: 375
13 :  80 00 77 94 81 00 4b 28 ff ff -- 924458923 -72.5dBm -- 2607ms  rcvd: 9481, console: 379
 2 :  80 00 77 93 c1 00 c3 74 ff ff -- 911915161 -82.0dBm -- 2505ms  rcvd: 93c1, console: 383
46 :  80 00 77 93 01 00 d5 20 ff ff -- 905391968 -68.0dBm -- 2606ms  rcvd: 9301, console: 388
35 :  80 00 77 92 41 00 ef dc ff ff -- 917935669 -71.0dBm -- 2507ms  rcvd: 9241, console: 392
40 :  80 00 77 91 81 00 a0 d8 ff ff -- 918940125 -72.0dBm -- 2604ms  rcvd: 9181, console: 396
49 :  80 00 78 90 c1 00 4e ca ff ff -- 913922607 -78.0dBm -- 2611ms  rcvd: 90c1, console: 401
11 :  80 00 78 90 01 00 58 9e ff ff -- 903888062 -70.0dBm -- 2505ms  rcvd: 9001, console: 405
 0 :  80 00 7f 8f 83 00 1b 1b ff ff -- 911413818 -83.5dBm -- 2610ms  rcvd: 8f83, console: 408
 5 :  80 00 7f 8e c3 00 21 e7 ff ff -- 906395874 -82.5dBm -- 2506ms  rcvd: 8ec3, console: 412
41 :  80 00 7f 8e 03 00 37 b3 ff ff -- 904389343 -68.0dBm -- 2607ms  rcvd: 8e03, console: 416
22 :  80 00 80 8d 81 00 58 ba ff ff -- 917434387 -71.5dBm -- 2608ms  rcvd: 8d81, console: 419
15 :  80 00 80 8c c1 00 62 46 ff ff -- 904890625 -68.0dBm -- 2509ms  rcvd: 8cc1, console: 423
16 :  80 00 80 8c 01 00 74 12 ff ff -- 915929138 -71.0dBm -- 2606ms  rcvd: 8c01, console: 428
33 :  80 00 80 8b 41 00 fc 4e ff ff -- 915427856 -71.0dBm -- 2508ms  rcvd: 8b41, console: 432
 7 :  80 00 80 8a 81 00 dd 2a ff ff -- 918438354 -70.0dBm -- 2605ms  rcvd: 8a81, console: 436
 0 :  80 00 80 8a 03 00 a0 d0 ff ff -- 911413818 -80.5dBm -- 2604ms  rcvd: 8a03, console: 439
21 :  80 00 80 89 43 00 f4 4c ff ff -- 903385376 -69.5dBm -- 2507ms  rcvd: 8943, console: 443
 3 :  80 00 80 88 83 00 d5 28 ff ff -- 922953186 -73.0dBm -- 2507ms  rcvd: 8883, console: 448
20 :  80 00 81 87 c3 00 82 61 ff ff -- 912919067 -72.5dBm -- 2603ms  rcvd: 87c3, console: 452
45 :  80 00 83 87 43 00 74 91 ff ff -- 919943604 -69.5dBm -- 7617ms  rcvd: 8743, console: 455
31 :  80 00 85 86 83 00 72 6c ff ff -- 910912109 -80.0dBm -- 2605ms  rcvd: 8683, console: 460
24 :  80 03 87 86 41 00 01 e0 ff ff -- 909406860 -80.5dBm -- 2604ms  rcvd: 8641, console: 461
37 :  80 00 87 85 c1 00 ad fa ff ff -- 920947083 -69.5dBm -- 2505ms  rcvd: 85c1, console: 464
 7 :  80 00 87 85 01 00 bb ae ff ff -- 918438354 -68.0dBm -- 2609ms  rcvd: 8501, console: 468
12 :  80 00 87 84 41 00 81 52 ff ff -- 916933533 -76.0dBm -- 2606ms  rcvd: 8441, console: 473
 9 :  80 00 87 83 c3 00 79 38 ff ff -- 920445374 -68.0dBm -- 2608ms  rcvd: 83c3, console: 476
38 :  80 00 87 83 03 00 6f 6c ff ff -- 908402893 -70.0dBm -- 2503ms  rcvd: 8303, console: 480
16 :  80 00 87 82 43 00 55 90 ff ff -- 915929138 -71.5dBm -- 2604ms  rcvd: 8243, console: 485
 2 :  80 00 87 81 83 00 1a 94 ff ff -- 911915161 -75.0dBm -- 2606ms  rcvd: 8183, console: 489
47 :  80 00 87 80 c3 00 20 68 ff ff -- 922451904 -72.0dBm -- 2606ms  rcvd: 80c3, console: 494
14 :  80 00 87 80 03 00 36 3c ff ff -- 910409912 -75.0dBm -- 2606ms  rcvd: 8003, console: 498
40 :  80 04 8d 7f 81 00 65 08 ff ff -- 918940125 -68.0dBm -- 2607ms  rcvd: 7f81, console: 501
31 :  80 00 8d 7e c3 00 b0 90 ff ff -- 910912109 -79.5dBm -- 2606ms  rcvd: 7ec3, console: 505
17 :  80 00 8d 7e 03 00 a6 c4 ff ff -- 921448364 -69.5dBm -- 2505ms  rcvd: 7e03, console: 510
42 :  80 00 8d 7d 43 00 f2 58 ff ff -- 923957153 -72.5dBm -- 2613ms  rcvd: 7d43, console: 514
 0 :  80 00 8d 7c 83 00 d3 3c ff ff -- 911413818 -82.5dBm -- 2609ms  rcvd: 7c83, console: 519
45 :  80 00 8d 7b c3 00 5b 60 ff ff -- 919943604 -72.5dBm -- 7211ms  rcvd: 7bc3, console: 523
 0 :  80 02 8f 7b 42 00 da 22 ff ff -- 911413818 -78.0dBm -- 2603ms  rcvd: 7b42, console: 526
24 :  80 00 90 7b 01 00 09 77 ff ff -- 909406860 -76.0dBm -- 2606ms  rcvd: 7b01, console: 528
26 :  80 00 90 7a 81 00 25 df ff ff -- 905894592 -74.5dBm -- 2602ms  rcvd: 7a81, console: 531
 5 :  80 00 90 79 c1 00 71 43 ff ff -- 906395874 -75.5dBm -- 2506ms  rcvd: 79c1, console: 535
18 :  80 00 90 79 01 00 67 17 ff ff -- 907399414 -70.0dBm -- 2505ms  rcvd: 7901, console: 539
19 :  80 03 90 78 81 00 a5 6d ff ff -- 926967651 -70.5dBm -- 2605ms  rcvd: 7881, console: 542
 9 :  80 00 90 78 03 00 36 45 ff ff -- 920445374 -71.0dBm -- 2507ms  rcvd: 7803, console: 545
37 :  80 00 90 77 83 00 01 ec ff ff -- 920947083 -68.0dBm -- 2509ms  rcvd: 7783, console: 548
31 :  80 00 90 76 c3 00 3b 10 ff ff -- 910912109 -77.0dBm -- 2606ms  rcvd: 76c3, console: 553
33 :  80 00 90 76 03 00 2d 44 ff ff -- 915427856 -67.5dBm -- 2606ms  rcvd: 7603, console: 557
 1 :  80 00 90 75 43 00 79 d8 ff ff -- 902381897 -69.0dBm -- 2603ms  rcvd: 7543, console: 562
42 :  80 00 90 74 83 00 58 bc ff ff -- 923957153 -75.0dBm -- 2603ms  rcvd: 7483, console: 566
40 :  80 00 90 73 c3 00 d0 e0 ff ff -- 918940125 -67.5dBm -- 2612ms  rcvd: 73c3, console: 570
50 :  80 00 90 73 03 00 c6 b4 ff ff -- 925462402 -82.5dBm -- 2508ms  rcvd: 7303, console: 575
39 :  80 00 90 72 43 00 fc 48 ff ff -- 912417358 -68.5dBm -- 2511ms  rcvd: 7243, console: 580
40 :  80 00 92 71 c1 00 35 8a ff ff -- 918940125 -66.5dBm -- 2603ms  rcvd: 71c1, console: 583
49 :  80 00 92 71 01 00 23 de ff ff -- 913922607 -72.5dBm -- 2605ms  rcvd: 7101, console: 587
 7 :  80 00 92 70 43 00 7f 40 ff ff -- 918438354 -67.5dBm -- 2603ms  rcvd: 7043, console: 592
16 :  80 00 92 6f c3 00 0b 8a ff ff -- 915929138 -68.0dBm -- 2610ms  rcvd: 6fc3, console: 595
40 :  80 02 8e 6f 03 00 0d c8 ff ff -- 918940125 -67.5dBm -- 2509ms  rcvd: 6f03, console: 599
26 :  80 00 8e 6f 40 00 11 d4 ff ff -- 905894592 -77.0dBm -- 2506ms  rcvd: 6f40, console: 598
21 :  80 00 8f 6e c1 00 78 f9 ff ff -- 903385376 -72.5dBm -- 2508ms  rcvd: 6ec1, console: 601
 9 :  80 02 8e 6e c3 00 2c ac ff ff -- 920445374 -72.0dBm -- 2602ms  rcvd: 6ec3, console: 601
30 :  80 00 8f 6e 41 00 63 61 ff ff -- 902884521 -72.5dBm -- 2607ms  rcvd: 6e41, console: 604
15 :  80 01 8f 6e 01 00 c4 fc ff ff -- 904890625 -70.0dBm -- 2606ms  rcvd: 6e01, console: 605
16 :  80 01 8f 6d 81 00 86 34 ff ff -- 915929138 -68.0dBm -- 2505ms  rcvd: 6d81, console: 609
41 :  80 00 8f 6d 01 00 37 fd ff ff -- 904389343 -72.0dBm -- 2604ms  rcvd: 6d01, console: 612
 8 :  80 01 8f 6c 81 00 b1 04 ff ff -- 908904663 -81.0dBm -- 2609ms  rcvd: 6c81, console: 615
 1 :  80 00 8f 6c 43 00 6b 63 ff ff -- 902381897 -70.0dBm -- 2606ms  rcvd: 6c43, console: 616
37 :  80 01 8f 6c 02 00 ff cf ff ff -- 920947083 -70.0dBm -- 2509ms  rcvd: 6c02, console: 618
19 :  80 00 93 6b 83 00 ac 32 ff ff -- 926967651 -73.5dBm -- 2611ms  rcvd: 6b83, console: 621
12 :  80 04 93 6b 43 00 33 60 ff ff -- 916933533 -73.5dBm -- 2603ms  rcvd: 6b43, console: 623
50 :  80 00 91 6b 00 00 0f 91 ff ff -- 925462402 -75.0dBm -- 2604ms  rcvd: 6b00, console: 624
19 :  80 00 91 6a c3 00 7b a6 ff ff -- 926967651 -76.5dBm -- 2505ms  rcvd: 6ac3, console: 626
 3 :  80 00 91 6a c0 00 2e f5 ff ff -- 922953186 -76.5dBm -- 2505ms  rcvd: 6ac0, console: 624
 2 :  80 00 91 6a 42 00 53 0f ff ff -- 911915161 -71.0dBm -- 2603ms  rcvd: 6a42, console: 629
30 :  80 00 91 6a 00 00 38 a1 ff ff -- 902884521 -72.5dBm -- 2601ms  rcvd: 6a00, console: 631
42 :  80 00 90 69 c2 00 67 73 ff ff -- 923957153 -74.5dBm -- 2601ms  rcvd: 69c2, console: 632
45 :  80 03 76 69 82 00 27 1e ff ff -- 919943604 -69.5dBm -- 2609ms  rcvd: 6982, console: 634
16 :  80 00 75 69 43 00 77 75 ff ff -- 915929138 -69.0dBm -- 2606ms  rcvd: 6943, console: 635
 7 :  80 01 75 69 40 00 88 77 ff ff -- 918438354 -68.0dBm -- 2605ms  rcvd: 6940, console: 635
30 :  80 04 74 69 03 00 85 0b ff ff -- 902884521 -78.0dBm -- 2505ms  rcvd: 6903, console: 637
20 :  80 01 74 68 c0 00 d2 6b ff ff -- 912919067 -69.5dBm -- 2503ms  rcvd: 68c0, console: 639
10 :  80 01 7b 68 80 00 0b 49 ff ff -- 913420410 -70.5dBm -- 2605ms  rcvd: 6880, console: 639
35 :  80 04 74 69 00 00 d0 58 ff ff -- 917935669 -68.0dBm -- 2607ms  rcvd: 6900, console: 637
40 :  80 00 75 68 01 00 2b eb ff ff -- 918940125 -68.0dBm -- 2503ms  rcvd: 6801, console: 643
 2 :  80 01 75 67 c3 00 dd bd ff ff -- 911915161 -71.5dBm -- 2602ms  rcvd: 67c3, console: 645
15 :  80 01 70 67 82 00 5f 05 ff ff -- 904890625 -70.0dBm -- 2604ms  rcvd: 6782, console: 647
29 :  80 05 78 67 41 00 10 c7 ff ff -- 924960205 -75.5dBm -- 2603ms  rcvd: 6741, console: 648
11 :  80 03 7a 67 03 00 5b 84 ff ff -- 903888062 -72.0dBm -- 2603ms  rcvd: 6703, console: 650
 0 :  80 05 7d 66 c3 00 e6 48 ff ff -- 911413818 -78.5dBm -- 2604ms  rcvd: 66c3, console: 652
22 :  80 02 75 66 81 00 6f f1 ff ff -- 917434387 -73.0dBm -- 2509ms  rcvd: 6681, console: 653
 5 :  80 02 74 66 82 00 4c 16 ff ff -- 906395874 -79.0dBm -- 2507ms  rcvd: 6682, console: 653
 1 :  80 07 79 67 42 00 77 a3 ff ff -- 902381897 -73.5dBm -- 2506ms  rcvd: 6742, console: 648

[davidefa]

A linear interpolation gives an error of +/-0.35°F ( the error has a sinusoidal shape ).
Attached the libreoffice calc sheet

P.S.
By the way what software/hardware are you using?

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[KevDev]

Thanks Davidefa!

A third of a degree error is acceptable I should think!  The sinusoidal error pattern is interesting.

P.S.
By the way what software/hardware are you using?

This is my software collecting raw data from the ISS using Node.js on a Raspberry Pi connected to an Adafruit RFM69 radio; the console readings were polled using a VP2 console data server (also that I wrote also running in Node.js on an rPi).

[KevDev]

From what johnd originally pointed out and what this article amplified:
https://www.manula.com/manuals/pws/davis-kb/1/en/topic/older-davis-stations

I'm the lucky owner of a VP2 system that was made for only two years 2004-2005 and that used an analog temperature sensor.  The article also recommends upgrading to a whole new ISS rather than try to upgrade the sensor which would also require a new SIM board.  Since all the other 'moving parts' of my ISS are 18 years old, this is probably a good idea.

For now, I'll use Davidefa's formula if the older type data is received and DeKay's if its new type data.

My ISS has done well; the only thing I replaced in those 18 years is the supercap.  It still works fine (at least I think I'm getting valid rain and wind readings).  I do see a new one coming in the not too distant future though.

[rdsman]

KevDev:

Is the value that the console is displaying supposed to be the decimal value of the temperature?  Please explain...

[KevDev]

It is the times 10 value.  So 215 would mean 21.5F.

[davidefa]

I've added a small sinusoidal term to reduce the error to +/-0.1°F ( with a few outliers ):

Code: [Select]

T=a*rcvd+b+sin((46849-rcvd)*2*PI/20415)Don't know how this correction performs outside the posted data interval ( 16°F-68°F )

 [ You are not allowed to view attachments ]

[KevDev]

I've added a small sinusoidal term to reduce the error to +/-0.1°F ( with a few outliers ):

Code: [Select]

T=a*rcvd+b+sin((46849-rcvd)*2*PI/20415)

Wow, that's great! 

If you look at the hex rcvd values you'll notice that they increment/decrement by 0x40 - so if you shift the value by >> 6 you'll get rid of some noise and the LSB will increment/decrement by 1 for each ~0.1 degree temperature change.  This might get rid of those outliers?

Yeah it would also be nice to test it at minus temperatures - we almost got there.

[kobuki]

I think you're dealing with an NTC's analog readout from the console. It's non-linear WRT temperature, rather, it's logarithmic. Approximating it using sine functions is weird. You could have a peek in the Meteostick WeeWx driver (written in Python) for an interpretation of other NTC-type sensors for Davis stations. I guess the older VP2 stations had analog sensors, you should be able to just copy the formulas.

[KevDev]

That does indeed look promising.  My initial attempt using his equations on a spreadsheet failed but I will pursue it more and get back with what I find.

Thank you!

[KevDev]

I played with the Meteostick WeeWx formula quite a bit and they do indeed apply to a NTC thermistor that Davis uses in their soil and leaf temperature/moisture sensors (thanks kobuki).  And even though the errors are linear, they grow over the sample temperature range and I cannot get it to be as accurate as davidefa's work.  So, I'm going to use davidefa's.  0.1 or so degree of accuracy (at least over the given sample range) is fantastic.

Thank you everyone!

[kobuki]

0.1 or so degree of accuracy (at least over the given sample range) is fantastic.

It's indeed fantastic, however, with these cheap NTCs you can't actually achieve 0.1 °C accuracy, more like 0.5 or so.

[BlueCoal]

KevDev, did you also have the same issue with the Humidity not reading correcting from the older unit?

[KevDev]

KevDev, did you also have the same issue with the Humidity not reading correcting from the older unit?

No, I believe every thing else worked as Dekay described.

[WeegeeNumbuh1]

Kinda reviving this thread but I want to provide additional reference:

Yeah it would also be nice to test it at minus temperatures - we almost got there.

So I actually ran into an issue a few months back and yeah the old analog ISSes encode their temperature data very differently than newer digital ISSes which is what Dekay and a lot of other people base their calculations on.
In my case since the console handles the conversion by itself before it sends anything to a datalogger I never needed to worry about these temp conversions until that whole situation showed up.
Not sure how this would affect the current hex conversions in this thread but this definitely threw a wrench into things until I decided just to get something that could understand something modern.