Power to the Pii-ple

The third revision of the Raspberry Pi can best be summed….

The third revision of the Raspberry Pi can best be summed up by the old adage of more of the same. A faster processor and Power over Ethernet capability were advertised – OEMsecrets tells you what you need to know.

Raspberry Pi’s are always sold via the ecosystem. This is a promise which the foundation, by and large, manages to keep: if you use a sufficiently recent version of RaspBian so that the new SOC is supported, the same memory card can also be used in older versions of the process computer. When looking at the thing from the top, not many differences can be seen. The most important change is the addition of the four pin header for the Power over Ethernet hat: it might cause problems with some cases. Other than that, the physical dimensions remain the same.

One interesting aspect is the heat spreader above the SoC. Eben Upton’s engineers used this opportunity to redesign the PCBs stack, thereby improving heat dissipation into the ground plane. This has two effects; first of all, the nominal maximum frequency has now increased to 1400 MHz from 1200 MHz. An important side effect is the ability of the process computer to sustain performance for longer runs – this can be shown in the figure which plots the temperature against the time when the process computer’s SoC is under heavy load.

The actual increase in processing power is rather modest. A short run of SysBench reveals the following results – the amount of RAM was not increased from the predecessor:

The Raspberry Pi foundation, of course, stays true to the MicroUSB port used for power supply. Some pundits claim that the plug is over strained – recently, MicroUSB plugs capable of carrying 3A have been provided by companies such as Wurth’s WR-Com series.

As for the actual power consumption, it increased a small bit. Our table contains some values which were obtained from a HP 6624A system power supply.

With that, it is time to sum up the first article on the new Raspberry Pi 3B+. Tune in soon for a second part looking at the network engine in more detail.

ST’s VL53L1CXV0FY/1 ST Distance

Measure distance with ST’s VL53L1X distance sensor

Creating “color” images is not new. Microsoft’s Kinect sensor introduced developers to getting spatial information: a trick which STM now make manageable via their laser-based distance sensor monoliths which are ideally suited to drone landing sensors, distance-sensitive ignitors and other trinkets.

All in one…

Unlike the sensor used in the Kinect, ST’s sensor is “one-dimensional”. The optical window at the top of the chip acts as viewfinder and emitter, while distance to “objects” in front of the detector is returned as a one-dimensional value (think: something is 50cm away from me). Furthermore, the use of LASER technology makes the system almost completely independent of the target material – the color-related problems known from classic IR components should not occur here.Host-Sensor connectivity is accomplished via the I2C bus: sadly, ST does not expose an address selector, thereby limiting you to one sensor per bus controller. The actual communication protocol is described in a seperate document: as ST loves to change its URL schemes, simply google for UM2356 to find it. Furthermore, a driver written in C is made available to aid implementors.


While current consumption is moderate in the range of less than 20mA when active, users must be aware of the maximum supply voltage of 3V5. This makes integrating the system into 5V I2C busses difficult – a level shifter made up of two FETs is a workaround (see directionalLevelShifter and application-note).

The inclusion of gigabit ethernet raised quite a few eyebrows: after all, the actual SOC is not able to provide more than about 480 Mbits of total bandwidth to all of the peripheral devices. In practice, this limitation shows up doing iperf runs:

Calibrate me!

Most sensors require modifications to case design: without a cutout “to look out from”, all kinds of strange problems occur. ST simplifies this by a dedicated calibration routine, which should be run on every unit in the factory. This also weeds out individual optical differences in the “window”, and accounts for any changes caused by reflowing.

Another nice aspect is the ability to set the “region of interest”. While the field of view, by default, is quite wide, the optical array can be tuned to limit it. In an eery similarity to the above-mentioned Kinect, detection range also is specified in “classes”.

The only disadvantage of the part is the insanely small footprint. ST uses a non-leaded case (Optical LGA) which is but 4.9×2.5×1.56 mm small: while the package can be reflowed with ease, fitting it to a prototype using a soldering station is borderline impossible.

As with all new chips, availability is an issue. On OEMsecrets, prices range from 2.8€ to 5€ in small quantities – as always, a price comparison is your wallet’s friend.

TLV7011 Series Comparator from Texas Instruments

TLV7011 Series Comparator from Texas Instruments

Digital is not everything: in real life, one sometimes needs a comparator. Texas Instruments recently-introduced TLV70x1 series provide a cheap and space-conscious solution for this problem.

The traditional knee-jerk reaction to a problem requiring a comparator is a great indicator of your age; some will grab an LM324, others will go for an LM741. Both of these are opamps, who require quite a bit of external “diddling” before they can act as a reliable comparator. This not only increases BOM size and cost, but also wastes space on the board.

Go dedicated

TI’s TLV70x1 family is a set of four ICs, each of which contain one comparator. The most outstanding attribute is the small size; the Extra Small Outline No-Lead (aka X2SON) package, described here, is but 0.8×0.8mm small. For prototyping, a classic SOT23 case is also available, which can be soldered by hand with some practice.

Generally, the parts are optimized to limit BOM changes. First of all, a supply voltage range of 1.6V to 5.5V means that the chip is very likely to “blend into” your environment. Benefit number two is an internal hysteresis to the – temperature dependent – tune of 4mV, thereby eliminating the need for a feedback resistor. One ambivalent aspect of the TLV70xx family is their capability to drive and sink insane amounts of current. Short-circuit values are in the range of 50mA, which means that most LEDs and even longer PCB traces can be driven directly. Of course, this also means that a bypass capacitor is recommended – the knife cuts both ways.

Greetings from the Kelly family

Traditionally, small part number deviations meant a change in the amount of chips in the case. This is not the case for the TLV family: the TLV7011 and 7031 have push-pull outputs, while the other ones use the open-drain principle. Furthermore, TLV7011 and TLV7021 use 5 Microamps of current and offer a propagation delay of 260ns, while the TLV7031 and TLV7041 need 335 Nanoamps at 3 Microseconds of propagation. Be aware that the TLV70xx series, being quite young, shows a tremendous price spread: as of this writing, quantity one prices range from 17 to more than 50 cents. Furthermore, finding datasheets can be difficult. But, as always, OEMsecrets to the rescue – simply follow the links in the table for more comparator goodness!