How to speed up serial communication on Windows

Posted on By Charity Carter

Changing the latency timer on a Windows PC can reduce the delay between transmitting two commands. Here is a step-by-step guide on how to do this!

  1. Open the Device Manager > Port (COM & LPT) > USB Serial Port (COM7). Note that the COM port number will likely be different on your machine.
  2. Right-click USB Serial Port and select Properties then navigate through
    Properties > Port Settings > Advanced.
  3. Using the Advanced tab, we can adjust the Latency Timer.
  • Step 1: Device Manager
  • Step 2: USB Port Properties
  • Step 3: Latency Timer

The latency timer controls the time interval between two commands in serial communication. We can confirm this by observing the communications signal on an oscilloscope.

  • Latency Timer set to 16ms
  • Latency Timer set to 8ms
  • Latency Timer set to 1ms

In the above, blue lines are commands sent from the PC and red lines are the Qontrol hardware response. We used two Q8b modules in this experiment, hence there are two commands and two responses.

And that’s it! We hope this short tutorial has helped you make the most of your Qontrol modules. If you have any questions, as always, please contact us and we would be happy to help!

How to connect to your chip

Posted on By Josh

This question comes up often. In this post, we outline some of the different approaches and discuss the interposers which we stock for various scenarios. If none of our existing interposers meet your needs, please contact us with your special product request.

We stock a variety of interposer PCBs. These take in the bulky 60 or 68-way cables from our line of docks and break them out into smaller connectors for wiring your devices. Most interposers present two or more identical output connectors. Some contain integrated patch panels, to allow manual re-wiring of the device. Others are directly wired, and rely on reconfiguration in software.

Continue reading How to connect to your chip

Avoiding common-ground electrical cross-talk

Posted on By Josh

Complex photonic devices require many electrical connections. A quick way to save a lot of connections is to use a common ground wire for several electro-optic devices (e.g. heaters, or photodiodes). For N devices, this saves N – 1 connections, which can translate to significant reductions in wire-bonding or multi-point probe size, and ultimately to savings in time and money.

Continue reading Avoiding common-ground electrical cross-talk

How to use a push-type output

Posted on By Josh

Push-type outputThe push-type, class-B, or open-emitter, amplifier output stage offers two main benefits: it can output 0 V when powered from a single supply, and it can drive very large currents. This stage features in our Q8 driver,  which uses MOSFET output elements. The basic structure of a push-type output stage is shown. Continue reading How to use a push-type output