ANT Forum

I am developing a sensor using the Bicycle Power Profile and am seeing a few single RX Failure msgs per minute on the ANT Display Simulator. After about three minutes the RX Failures they bunch up: for example 2, then 4, then 8, then a drop to Search. The Search reconnects quickly and the pattern repeats, but the data dropout of several seconds is unacceptable.

The C7 transmitter on my sensor and the ANT USB stick controlled by ANT Display Simulator are 18 inches apart on my desk - no relative motion - and are set to default power. I send data packets at 4 per second. Most of the packets are Wheel Torque. Every fifth packet is Power Only. Every 60 packets alternates Manufacturer's Data and Product Data. I have captured the packets sent around the point of failure and see correct format, correct checksum and the RTS pulse indicating that the C7 module has received the packet.

Any ideas about the source of these dropouts would be greatly appreciated.      

That sounds as if the sensor and display get out of phase.
Did you double check that you set the channel period to the correct value as of the device profile?      

Thanks for your helpful and instant response. The msg period is set to 8182 with the ANT radio frequency configuration command 0x45. I assumed that 8182/32768 = 4.0049 Hz is the rate at which the C7 module sends messages to the remote slave. I send msgs from my MSP430 to the C7 at 4 Hz as measured by the MSP430 clock; do I need to send these at the 4.0049 Hz rate? If so, I have missed something basic: how can the MSP430 and C7 clocks be synchronized? Can I send to C7 slightly faster than 4.0049 to ensure something is always available at 4.0049? Is there some chunk of the documentation that I have completely overlooked?      

Oops, that would be 0x43 to set the channel period.      

Hi dwilhide,

8182 is the correct channel period for bike power.

If the MSP430 was too slow to send the next message to the C7, then the previous message would simply be retransmitted. However if a new message is being written to the buffer at the point when a message should be being sent, there could be a conflict. So try waiting for the EVENT_TX messages from the C7 and using those as triggers to send the next message to the C7 for transmission. (See 9.5.6 of the ANT Message Protocol and Usage document).

Also, if you haven't already seen it, the ANT Basics video (here: http://www.thisisant.com/developer/ ) contains very useful background knowledge on how ANT transmissions work.

If that doesn't fix it, then please post your logs and I'll take a look.

Thanks,

Kat      

Synchronizing the msp430 data-packet transmission to the EVENT_TX response from the C7 solves the problem. Thanks to old_man_biking and Kat.