Improvements for the Yocto-PWM-Tx

Improvements for the Yocto-PWM-Tx

After four years of operation, we rejuvenate the Yocto-PWM-Tx this Spring, with hardware and software improvements. It naturally stays 100% compatible with the original version. Here is a small overview of what's new.





Hardware improvements

The most observers among you may have noticed that in Fall 2016 we already performed a small hardware update. Since then, the circuits have a Rev. B mark. At that time, we added a few components to reduce unwanted electromagnetic emissions and to protect outputs against possible transient overvoltages.

In a few weeks, you'll find the Rev. C mark. This new revision includes mainly the addition of a clock chip providing a much better accuracy for the generation of specified frequencies. Indeed, originally, we aimed at the accuracy of the duty cycle for this product, and not at the accuracy of the frequency itself. But as time went by, other applications for this module appeared, for which a good frequency accuracy was a must. Thus, this new revision now guaranties an accuracy of 0.1 per thousand on the frequency.

Look for the differences between these three generations of the Yocto-PWM-Tx...
Look for the differences between these three generations of the Yocto-PWM-Tx...



Software improvements

Even if you don't buy a new Yocto-PWM-Tx, you can benefit from a few improvements by simply updating your module firmware, as we reworked it in depth.

Rational frequencies

The previous firmware never returned a frequency which wasn't a multiple of 1 Hz. For more accuracy, you had to work with the period, which was specified to the millisecond. You can now configure and retrieve the frequency as a rational number up to the millihertz.

Duty cycle transitions

Since the first versions of the product, you could ask the module to generate a linear transition between two duty cycles. But up to now, the smoothness of the transition depended on the module load, and was therefore not guarantied. This new firmware implements an accurately linear, step-by-step computation, up to about 31 kHz. Above 31 kHz, the duty cycle isn't modified for each step, but accurately each 62.5 us, which nevertheless guaranties a good linearity.

Step-by-step duty cycle transition, from 10% to 90%
Step-by-step duty cycle transition, from 10% to 90%



Frequency transitions

For applications driven using the frequency, we also introduced the possibility to generate linear frequency transitions (constant cyclic acceleration). As for duty cycle transitions, they are computed step-by-step up to 31 kHz. Above 31 kHz, the frequency is accurately adapted each 62.5 us.

Example of a step-by-step linear frequency transition
Example of a step-by-step linear frequency transition



Pulse sequences

Customers also asked us whether it was possible to use the Yocto-PWM-Tx to create a pulse sequence containing a fixed number of cycles. It's now possible: either from the idle state or from a basis cyclic state, you can generate a fixed number of pulses in frequency mode or with a specified duty cycle. Note that there as well, the exact count is possible up to 31 kHz only. Above, the duration of the pulse train is restricted to a multiple of 62.5 us.

Example of a sequence of 4 pules at 40%
Example of a sequence of 4 pules at 40%




1 - univ. helsinki pedro Monday,may 07,2018 15H45

Some time back (I think a couple of years ago) I asked if it would be possible to control the phase shift between the two channels or at least keep them in sync. I would like to produce two trains of pulses at the same frequency, while being able to adjust the duty cycle and the phase shift between channels: a simple example case would be to have 50% duty cycle, with pulses alternating in the two channels. Another case would be to have the pulses in the two channels in-sync at the leading edge but with different duty cycles. For this later case a software trigger to start both channels simultaneously could be enough... The answer was we may implement this in the future... so I am asking now is this feature now available, can be expected to be added in the near or far future...?
Feature added or not, your modules and software are beautifully engineered and built! Thanks!

2 - mvuilleu (Yocto-Team)Tuesday,may 08,2018 9H17

@pedro With the new PWM generation system it should actually be not too difficult to implement your request, as we now have the ability to generate precisely timed squared wave forms, as long as the frequency is under 31kHz. What frequency do you need for your application?

3 - univ. helsinki pedro Tuesday,may 08,2018 22H31

@mvuilleu Thanks for the very fast answer. The application is PWM dimming of LEDs. We want to test several frequencies, but in the range 10Hz to 1kHz. At the moment I am using LED drivers from RECOM's RCD-24 and RCD-48 series. I am using a Yocto-PWM-Tx (older) for PWM dimming and an a Yocto-0-10V-Tx for CC dimming. These LED drivers from RECOM support the use of PWM and CC in combination, so at the moment we can change duty cycle and frequency keeping constant the time-averaged irradiance (amount of light). We are starting in a few weeks a small experiment using a single channel of white light. Later on, we would like to play by mixing light of two colours in different ways. The objective is to try to assess the effect of different dimming approaches on photosynthesis, as LEDs are fast becoming popular for plant cultivation.

Yoctopuce, get your stuff connected.