Start Sender (Pro)
Start Sender records the start time and activates Photo/Video/Live Finish on another device. It can also be used as a remote control to start and stop the video recording. Start Sender has two modes:
Direct
The devices are in direct contact with each other over WiFi and can synchronise the clocks directly. For short distances, no extra hardware is needed, but for distances over c:a 30 m an external WiFi network is required (but not internet access).
Cloud
The devices communicate with online time servers and iCloud. An Internet connection is therefore required, either over a cellular/mobile networks, or via a WiFi connected to Internet. There are two different version of the cloud mode (private and public) with a slightly different setup, but with the same functionality.
Synchronization and setup
Before using the Start Sender, the devices must be synchronized to establish the difference between the internal clocks and to set up the communication. In Cloud mode this is done automatically in the background. In Direct mode you must start the sync manually.
Direct Mode
- Turn on WiFi on both devices (plus Bluetooth if you are running without an external network)
- Open StartSender from the main menu on one device.
- In SprintTimer on the other device, go to Start Setup and choose the mode Start Mode: Start Sender. Tap the Synchronize button when the text says "Start sender found". Synchronization usually takes 10-15 s.
- When it says "Ready to run" you can close the Setup.
Start Sender will continuously update the clocks, so there is no need for resyncing, unless the communication is lost.
A video of the setup ->
Cloud Mode
- Check that you have Internet access on both devices.
- Check in your account in the Settings app that SprintTimer allowed to use iCloud.
- If you are using a mobile network go to Cellular (green radio mast icon) in the Settings app and turn on Mobile data. Scroll down and check that SprintTimer is allowed to use mobile data.
- Open StartSender from the main menu on one device and set the "Start Sender Mode" to "Cloud" in the start setup.
- Open SprintTimer from the main menu on the other device and set the "Start Mode" to "Start Sender" and set the "Start Sender Mode" to "Cloud" in the start setup.
With public cloud you can use devices with different Apple-accounts. But to set it up you must first check the unique Start Sender ID in the start setup in Start Sender. Then type that ID in the start setup in SprintTimer on all finish line devices.
Start
A start in Start Sender will open the camera in the finish line device, and you can then start the recording the usual way. If you want the finish device to be completely autonomous go to Set Finish on the finish device and set Start recording to Time or Motion and turn on Auto finish. Alternatively, you can turn on Remote recording in the finish setup on the Start Sender device. Then you can start and stop the recording from start sender.
The start in Start Sender works similar to when you use only one device (see the Start guide). The differences are that there is no Hand+Mic, but instead, there is a Start on motion, which uses the camera to detect motion.
If you use Self start, Start Sender will also measure the reaction time. This is described more in detail in this blog post.
Feedback
In Direct mode there is some feedback between the devices. The start and activate buttons are disabled when the receiver is not ready. You can also activate the sound start from the finish. If the connection is broken both sides are notified.
In Cloud mode each side communicates with a server and you will get feedback if that connection is OK, but not necessarily information about whether the other side is active. Sending a start is, therefore, a bit like sending an email. There will also be a few seconds delay before the finish gets the start time (this delay does not affect the accuracy).
Back up start
On the finish side there is a small "Hand Start" button. It will start the Photo/Video finish as if it was a single device with manual start. However, if it gets a start time from Start Sender after the button is pressed, but before the recording has stopped, that time will be used instead. So if you press that button at the start you will be sure to always have a time, even if the network is unstable. If the "Hand" time is used, the running clock in the camera view is shown in grey. The button will use the same press/release setting as the hand start.
Apple Watch
The Apple Watch can be used similar to Start Sender. See the start guide for more details.
Latency/accuracy
All networks have delays (latency) which affect how accurately the clocks can be synchronized. The latency is therefore reported. In direct mode is the synchronization handled by the finish unit and the latency is reported there. In Cloud mode are the devices synced separately and the latency is reported on both sides. The total latency is therefore the sum of the two. The latency represents the maximum possible error, in practice is the accuracy usually much better. The quality of the network will affect the latency, for example is 4G usually better than 3G.
The direct mode also has an "age" parameter, it will increase to around 1.0 and should stay there. If it goes significantly higher it is a sign that the network is slow and the synchronisation isn't updating properly. In the cloud mode there is instead an "offset" parameter. It shows the difference between the device time and the network time. It doesn't directly affect the accuracy, but if it is > 1 s it is a sign that the synchronisation might have problems.
To test the connections and synchronisations you can do a zero test.
Overview
| Direct | Priv Cloud | Pub Cloud | |
| WiFi Com | Yes | Yes | Yes |
| Cellular Com | No | Yes | Yes |
| Internet required | No | Yes | Yes |
| Remote Control | Good | OK | OK |
| Accuracy | High | Good | Good |
| Pro accounts | One | One | Multi |
This page is also available at sprinttimer.app/support