7 ms·

Does anyone know of a solution that can go down to the 5khz range? Older (...and even newer) gym equipment uses the gymlink protocol for heart rate monitors ins

Does anyone know of a solution that can go down to the 5khz range? Older (...and even newer) gym equipment uses the gymlink protocol for heart rate monitors instead of low power Bluetooth and friends, and very few monitors support it anymore. I wanted to try to make a converter but couldn't find anything to output in that frequency.

octopoc 5y ago
I think it's pretty easy to make circuitry to shift a radio's frequency. If you did that with LimeSDR you'd still get the same bandwidth but it would be shifted into a different range.
ronsor 5y ago
At 5000 Hz, you could probably just rig up a sound card with a mic input.
- Blackthorn 5y ago
  I need to output the 5khz, not input it. Would I be able to do that with a sound card in a small form factor? The idea is to have a small box that can convert my heart rate monitor to something that the gym equipment can understand.
  - ronsor 5y ago
    I believe attaching an antenna to the card's output could work. For small form factor, a USB sound card and a Raspberry Pi is a possibility.
  - jpindar 5y ago
    I've used a cell phone as an audio signal generator for testing transmitters. There are apps for sending a continuous signal, and I assume it would be easy enough to write one for sending a modulated signal. BTW, this is one reason why I won't buy a phone without an audio jack.
jquast 5y ago
Ham It Plus can go upconvert as low as 300Hz, compatible with any SDR you just shift the frequency in software https://support.nooelec.com/hc/en-us/articles/360005812474 https://support.nooelec.com/hc/en-us/articles/360005812474
- Blackthorn 5y ago
  Guess I didn't make it clear and that's my bad. I need to output 5khz, not input. The input is a more modern Bluetooth protocol.
  - jquast 5y ago
    sorry maybe we misunderstand each other, I just got my license last year but this FAQ link reads, "Is the Ham It Up capable of transmitting as well as receiving? Even on lower frequencies? -- Yes, it is bidirectional, so you can transmit and receive on any frequency within range, provided that you have a compatible transceiver, like the HackRF One. "
  - user-the-name 5y ago
    Why not just use audio out then?
ThrowawayR2 5y ago
The only thing I can think of that goes that low out of the box is the old Ettus Research USRP1, B100/B110, or E100/E110 SDRs combined with both a LFRX daughtercard and LFTX daughtercard, which are DC - 30 MHz. The SDRs themselves can occasionally be found on eBay and the daughtercards are still sold directly by Ettus Research or themselves occasionally can be occasionally found on eBay.
moftz 5y ago
5KHz is pretty low, it would be difficult finding anything in the ham category because no ham bands are that low. You would need to probably build your own receiver. The good news is that 5KHz is super low frequency and could easily be received with a crystal detector. Antenna connects to an LC resonator centered at 5.3KHz, pass the result of this through a diode and then into a microcontroller. Many have analog input pins and analog comparators built-in that can trigger an interrupt. You would need to figure out what voltage level you expect to see from the detector when a heart beat signal is sent and then apply that voltage to the other side of the comparator. Some microcontrollers even have a real analog voltage output that could allow you to adjust the voltage through software. The microcontroller would then trigger an interrupt and do something every time a heart beat signal is received (send it through serial to a PC, compute heart rate, display something on a LED screen, etc). If you need to broadcast at 5.3KHz, that's pretty easy too. There are numerous designs out there for a basic CW transmitter (https://makerf.com/posts/ten-minute-transmitter https://makerf.com/posts/ten-minute-transmitter). You may have trouble finding a crystal centered at your 5.3KHz frequency.
lxe 5y ago
Try an upconverter like this https://www.nooelec.com/store/ham-it-up.html https://www.nooelec.com/store/ham-it-up.html or https://airspy.com/spyverter-r2/ https://airspy.com/spyverter-r2/
jmrm 5y ago
I find totally rare that these devices works at 5kHz. instead of 5MHz or 500Khz (for example). At 5kHz you would need in theory huge antennas to being able to transmit and receive the signal correctly, and hundreds of kHz frequencies are totally achievable even with the most basics mid 1900s telecom systems. If you know the data to send, and you are totally sure the data is sent electromagnetically at 5kHz, you can modulate in as sound in a computer and play it in a PA system connected to a long cable,

octopoc 5y ago

I think it's pretty easy to make circuitry to shift a radio's frequency. If you did that with LimeSDR you'd still get the same bandwidth but it would be shifted into a different range.

ronsor 5y ago

At 5000 Hz, you could probably just rig up a sound card with a mic input.

Blackthorn 5y ago
I need to output the 5khz, not input it. Would I be able to do that with a sound card in a small form factor? The idea is to have a small box that can convert my heart rate monitor to something that the gym equipment can understand.
- ronsor 5y ago
  I believe attaching an antenna to the card's output could work. For small form factor, a USB sound card and a Raspberry Pi is a possibility.
- jpindar 5y ago
  I've used a cell phone as an audio signal generator for testing transmitters. There are apps for sending a continuous signal, and I assume it would be easy enough to write one for sending a modulated signal. BTW, this is one reason why I won't buy a phone without an audio jack.

jquast 5y ago

Ham It Plus can go upconvert as low as 300Hz, compatible with any SDR you just shift the frequency in software https://support.nooelec.com/hc/en-us/articles/360005812474 https://support.nooelec.com/hc/en-us/articles/360005812474

Blackthorn 5y ago
Guess I didn't make it clear and that's my bad. I need to output 5khz, not input. The input is a more modern Bluetooth protocol.
- jquast 5y ago
  sorry maybe we misunderstand each other, I just got my license last year but this FAQ link reads, "Is the Ham It Up capable of transmitting as well as receiving? Even on lower frequencies? -- Yes, it is bidirectional, so you can transmit and receive on any frequency within range, provided that you have a compatible transceiver, like the HackRF One. "
- user-the-name 5y ago
  Why not just use audio out then?

ThrowawayR2 5y ago

The only thing I can think of that goes that low out of the box is the old Ettus Research USRP1, B100/B110, or E100/E110 SDRs combined with both a LFRX daughtercard and LFTX daughtercard, which are DC - 30 MHz. The SDRs themselves can occasionally be found on eBay and the daughtercards are still sold directly by Ettus Research or themselves occasionally can be occasionally found on eBay.

moftz 5y ago

5KHz is pretty low, it would be difficult finding anything in the ham category because no ham bands are that low. You would need to probably build your own receiver. The good news is that 5KHz is super low frequency and could easily be received with a crystal detector. Antenna connects to an LC resonator centered at 5.3KHz, pass the result of this through a diode and then into a microcontroller. Many have analog input pins and analog comparators built-in that can trigger an interrupt. You would need to figure out what voltage level you expect to see from the detector when a heart beat signal is sent and then apply that voltage to the other side of the comparator. Some microcontrollers even have a real analog voltage output that could allow you to adjust the voltage through software. The microcontroller would then trigger an interrupt and do something every time a heart beat signal is received (send it through serial to a PC, compute heart rate, display something on a LED screen, etc). If you need to broadcast at 5.3KHz, that's pretty easy too. There are numerous designs out there for a basic CW transmitter (https://makerf.com/posts/ten-minute-transmitter https://makerf.com/posts/ten-minute-transmitter). You may have trouble finding a crystal centered at your 5.3KHz frequency.

lxe 5y ago

Try an upconverter like this https://www.nooelec.com/store/ham-it-up.html https://www.nooelec.com/store/ham-it-up.html or https://airspy.com/spyverter-r2/ https://airspy.com/spyverter-r2/

jmrm 5y ago

I find totally rare that these devices works at 5kHz. instead of 5MHz or 500Khz (for example). At 5kHz you would need in theory huge antennas to being able to transmit and receive the signal correctly, and hundreds of kHz frequencies are totally achievable even with the most basics mid 1900s telecom systems. If you know the data to send, and you are totally sure the data is sent electromagnetically at 5kHz, you can modulate in as sound in a computer and play it in a PA system connected to a long cable,