ANT Forum

Hi,

I am developing an application that displays heart rates from ANT+ HRM devices, the application will be used in a group environment with up to 20 different HRM devices. Is it possible to have more than 8 HRM devices connected to one ANT+ USB? It is my understanding that the ANT+ USB is limited to 8 channels. Is there a way to have the HRM devices share channels? Or increase the number of channels available to the USB?      

Hi,

Continuous scan mode would allow you to receive and/or respond to as many ANT master transmissions as possible on a single RF frequency. ANT master's isochronous adaptive coexistence means they'll automatically attempt to share the airtime in a way that they can all be heard.

You may find the app note here.

Also, I'd like to note that there are many RF issues which can occur in a group setting, such as directionality of the HR transmitters, water in the human body blocking the signal, positioning of the receiver(s), etc.      

Hi admin,

I think you are not in the same page what Bob means. I also have the same problem that I am unable to read data concurrently from more than 8 devices.

My developing context is, I have an android app running on a device (samsung note3 which is ant+ supported). This app is using ant's official android api to connect ant devices (hrm devices only).

When this app is receiving data from 8 ant+ transmitters (wahoo tickers) then it is working fine and displaying data concurrently. But when I hit an attempt to connect 9th device than it is giving me the error "CHANNEL_NOT_AVAILABLE".

I have gone through the link you have suggested but it was not helpful for android app purpose.

Can you please let me know the fact that if there is any limitation of channels or I can't read data from more than 8 devices at a time?

Thanks      

Hi Simon,

The number of ANT channels available is dictated by the device's firmware. On many Android devices that limit is currently set to 8.

For Android, the onboard chip won't support continuous scan mode as it needs to support concurrency with other wireless protocols such as Wi-Fi or Bluetooth, but you can use a background scanning mode channel instead. While this would require some re-architecture, it would allow your device to listen to as many transmissions as the radio on the phone could give time for. The ANT+ Plugins Sampler shows an example of this in the "Async Scan Demo" activity.

Another option would be, assuming your device supports USB OTG, plug an ANT+ USB stick in and install the ANT USB Service. This would either add another 8 channels and/or give you a device that supports continuous scan mode.

Cheers