EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: sequoia on May 16, 2020, 09:09:16 pm
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I was looking into logging to computer data from various wireless weather/temperature sensors I have scattered around.
Initially it seemed that cheap ($1-2) receiver modules available all over the net might do just fine
[attach=1]
I hooked up the receiver to a logic analyzer and was able to clearly capture transmissions from the weather sensors (receiver module transmits data only when there is transmission, otherwise data output is "idle"...)
However, this was with receiver hooked up to a lab PSU, when I tried hooking it up to a Arduino Nano (clone) I noticed that when powered from the nano Vcc pin, the receiver was continuously receiving "noise". Seems like the cheap receiver cannot handle any noice in the Vcc input... (Adding decoupling caps to receiver input helped only slightly reducing the noise output from the receiver...)
I guess this is to be expected with these very cheap receivers (without a clock crystal)?
This brings me to my question is there any "good" receiver modules floating around that can tolerate "noisy" power source/environment? It would need to be module that support outputting "raw" OOK signal, so that can then use a MCU to decode wildy differing data formats (line codings) that may be used by different proprietary systems...
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These devices are very susceptible to noise. If you check long enough, you can see that the receiver will get fair amount of spur outputs. If you are using Arduino, you can find library code that uses encoding systems to reject the noises. As long as you don't need high data rate, it should work. I have used these in a simple remote light switch application. I used a PIC16 MCU and implemented my own noise rejection code. Another thing you need to consider is that these devices does not have very long range. You'll need to add antenna to both the transmitter and the receivers. I have noticed, that I was able to get about 10 meter range with my setup.
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yes those cheap $1 are susceptible to noise just because they are unfiltered, raw and auto gain receiver. the rest you have to do yourself. simply reject any signal pulses that is less than X ms/us width then you should be good. the thing i like about them is they are RAW radio so what i see is RAW! and i like RAW i can deal with processing them later. the bad thing is they are very slow only good for few Kbps. so if you want faster and preprocessed (digital) signal output, you can go with something like IC CC1101 or NRF24L01, they are older cheap radio version and you'll need to read datasheet for codes to make them work. if you want to get fancy go with more modern LoRa or wifi/bluetooth version (no experience). i bought the 433MHz cheapy like 10 pairs years ago and i have one working as door bell controlled from either pic10f206 or attiny13 iirc quite reliably for years now (multiple transmission and checking to pass as a valid signal and ring the door) after being sick with multiple purchase and failed on me the cheap crap of wireless door bell. i even built the best antenna for them and later have to crippled the transmitter antenna so my signal will not go all around broadcasting my signature to the neighborhood.
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"RXB6" receiver modules seems to be noticeably better. These can tolerate interference much better, likely thanks to the cover/shield over the receiver components (and it's use of a clock crystal):
[attachimg=2]
[attachimg=1]
(these seem to sell in $2-3 range, so still very inexpensive)
I have this module working fine, directly powered from Vcc of Arduino Nano (clone) and "DATA" pin hooked to D2 pin on the Arduino.
This one seems to suffer from the automatic gain control of the receiver as well, if there is no transmissions for a while, gain control will "open" up all the way and when transmission is received it overloads the receiver and it takes a while for the gain control to react....
I have some Hideki (TS33C) sensors (these have been sold under various "brands" like Honeywell, Mead Instruments, etc...), and these seem to start transmitting with hardly any delay, so "RXB6" often fails to receive first few bits accurately.... but since these sensors repeat the data 3 times, it catches the subsequent two transmissions rather reliably (while first transmission it seems to receive completely only about 10-20% of the time).
Module that has ability to control the gain would be really nice... or just module with better AGC might be all that is needed (?)
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Module that has ability to control the gain would be really nice... or just module with better AGC might be all that is needed (?)
maybe controlling psu to the module is a way to control when to receive or not. sending few preamble bits will settle down the gain stage before sending real data... still you need to check your data validity in some way (redundancy, CRC, parity) in case there is interfering signal within the bandwidth.
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I'm looking to continuously monitor/receive transmissions (no control over the transmit side), so need something that has good (fast) AGC on the receiver. Or I guess alternatively, a receiver where gain can be controlled (so can tune out the background "noise") should work as well?
I had not given LoRA modules a thought, since they're tranceivers (and I just need a receiver), but looks like some of those have "raw" output for ASK (AM) signals, like SX1278 based modules: https://www.open-electronics.org/using-lora-shield-in-packet-mode/ (https://www.open-electronics.org/using-lora-shield-in-packet-mode/)
Aliexpress/etc. seems to have lot inexpensive ($10-15 range) SX1278 based modules available, and even with SMA connector for external antenna which is good!
For example:
[attachimg=1]
(https://www.banggood.com/LoRa-SX1278-433MHz-Wireless-RF-Module-IOT-Transceiver-p-1410555.html (https://www.banggood.com/LoRa-SX1278-433MHz-Wireless-RF-Module-IOT-Transceiver-p-1410555.html))
Seems like some of these LoRa modules might be way to go. Since they don't seem to be really any more expensive than some of the nicer receiver modules like ones from Aurel: https://www.aurelwireless.com/wp-content/uploads/shortform/650200590G_sf.pdf (https://www.aurelwireless.com/wp-content/uploads/shortform/650200590G_sf.pdf)
(and having SMA antenna connector already installed is a plus)
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I've used SI4432 as code grabber:
spi_w(0x27,rssi_treshold); // put average rssi+2db
spi_w(0x0d,0x1c); // GPIO_2 outputs ASK/OOK
have control over RBW and rx channels
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I've used SI4432 as code grabber:
spi_w(0x27,rssi_treshold); // put average rssi+2db
spi_w(0x0d,0x1c); // GPIO_2 outputs ASK/OOK
have control over RBW and rx channels
Thanks for the tip! SI4432 looks pretty much exactly what I was looking for, just ordered couple modules to test with.
Looks like SI4432 may be better choice than SX1278 based modules, as those dont often seem to expose DIO2 that provides the "raw" OOK output...
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Well there are a lot of thinks on the 433 Band. Here a quick screenshot:
[attachimg=1]
Well to decode all somethink more powerfull I guess is necessary.
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yesterday optimized my PSOC1/SI4432 setup now able to scan whole LPD band in 2ms !