Synchronization of cameras

[Miguelon]

Hi

I wish to synchronize several cameras, and I have not found the way to do it. 

Is there any HW solution (trigger) that could help in this?

Is there at least any SW solution that can maybe help?

I need to have the cameras capturing at the same time.

Kind regards,

Miguel

[Kim Janson]

I would try occasionally syncing them. Also it is not the same as image sensor. 

"It is noteworthy that the integration period for a thermal detector does not have the same impact on image formation as it does for a photon detector, such as a typical CMOS array. A photon detector converts incoming photons to electrons with near-instantaneous response time but only collects information from the scene during the integration period. In other words, high-speed phenomena (such as a strobed signal) can be missed entirely if the resulting photons are incident at a point in time when the detector is not integrating. A thermal detector, on the other hand, is always changing temperature in response to incident radiation. That is to say, it is always “active” regardless of whether or not it is being actively integrated. The integration period only refers to the time that resistance is being sensed by integration of current, not the time the sensor is actively responding to irradiance from the scene. The ability to detect high-speed phenomena is more a function of the detector's thermal time constant, which governs the rate of temperature change. For Lepton, the detector time constant is on the order of 12 msec, which means that an instantaneous irradiance change will result in a temperature change of the detector as shown in Figure 27.

 "

[Kim Janson]

maybe 

4.6.7 VID Video Freeze Enable State 

[Kim Janson]

Looks like it is actually even easier than that, just use SC 

9.2 VoSPI Channel

The Lepton VoSPI protocol allows efficient and verifiable transfer of video over a SPI channel. The protocol is packet-based with no embedded timing signals and no requirement for flow control. The host (master) initiates all transactions and controls the clock speed. Data can be pulled from the Lepton (the slave) at a flexible rate. This flexibility is depicted in Figure 14, which shows the use of a relatively slow clock utilizing most of the available frame period as well as the use of a fast clock that bursts frame data. Once all data for a given frame is read, the master has the option to stop the clock and/or deassert the chip select until the next available frame. Alternatively, the master can simply leave the clock and chip select enabled, in which case Lepton transmits discard packets until the next valid video data is available. 

[Miguelon]

Hi Kim

Thanks for your response.

However, I believe your suggestions could only help only for a synchronization in the communication, while what I´d like to synchronize is the trigger of the camera. 

Let´s say we have a buffer with the image. As far as I understand, all you can do with VoSPI is controlling how this buffer is transferred by SPI interface.

But what I want to control is the readout of the FPA state that is collected in the buffer. I understand these cameras work different to others, but I would say that there is a sampling process as in any other digital camera, and the buffer is sampled by some trigger event. These sampling trigger events is what I´d like to synchronize across the set of cameras.

Kind regards,

Miguel

[Miguelon]

The only way I see and I might try is to do some HW modification to use to try to use the master signals from one breakout board (power, masterclock, reset,...) to feed all the other leptons, and then other breakout boards only deal with communications.

Quite unsure if they will keep synchronize, but if they behave the same with same "master" signals, maybe there is a chance they keep synchronized...

Any comment is welcome.

Thanks in advance.

[Kim Janson]

I would suggest synchronizing all the cameras at same time and maybe using same oscillator for all cameras 

"9.2.2.3.1Establishing/Re-Establishing Sync

The basic process for establishing synchronization is listed below:

• Deassert /CS and idle SCK for at least 5 frame periods (>185 msec). This step ensures a timeout of the VoSPI interface, which puts the Lepton in the proper state to establish (or re-establish) synchronization.

• Assert /CS and enable SCLK. This action causes the Lepton to start transmission of a first packet.

• Examine the ID field of the packet, identifying a discard packet. Read out the entire packet.

• Continue reading packets. When a new frame is available (should be less than 39 msec after asserting /CS and reading the first packet), the first video packet will be transmitted. The master and slave are now synchronized. 

"

[Kim Janson]

how do you read many cameras at same time, Maybe just simply using CS and reading them a line at time would keep them synched?