Data retention is a funny thing. Atmel will gladly tell you that the flash memory in an ATmega32A will retain its data for 100 years at room temperature. Microchip says its EEPROMs will retain data for over 200 years. And yet, humanity has barely had a good grasp on electricity for that long. Heck, the silicon chip itself was only invented in 1958. EEPROMs and flash storage are altogether younger themselves.
How can these manufacturers make such wild claims when there’s no way they could have tested their parts for such long periods of time? Are they just betting on the fact you won’t be around to chastise them in 2216 when your project suddenly fails due to bit rot.
Well, actually, there’s a very scientific answer. Enter the practice of accelerated wear testing.
Charging an EV currently means making sure you find a station with the right plug. SAE International has now published what could be the end to the mishmash of standards in North America with the J3400 North American Charging Standard.
The SAE J3400TM North American Charging Standard (NACS) Electric Vehicle Coupler Technical Information Report (TIR), which just rolls off the tongue, details the standard formerly only available on Tesla vehicles. We previously talked about the avalanche of support from other automakers this year for the connector, and now that the independent SAE standard has come through, the only major holdout is Stellantis.
Among the advantages of the NACS standard over the Combined Charging System (CCS) or CHAdeMO is a smaller number of conductors given the plug’s ability to carry DC or AC over the same wires. Another benefit is the standard using 277 V which means that three separate Level 2 chargers can be placed on a single 3-phase commercial line with no additional step down required. Street parkers can also rejoice, as the standard includes provisions for lampost-based charger installations with a charge receptacle plug instead of the attached cable required by J1772 which leads to maintenance, clutter, and ADA concerns.
Now that J3400/NACS is no longer under the purview of a single company, the Federal Highway Administration has announced that it will be looking into amending the requirements for federal charger installation subsidies. Current rules require CCS plugs be part of the installation to qualify for funds from the Bipartisan Infrastructure Bill.
If you want to see how to spice up charging an EV at home, how about this charging robot or maybe try fast charging an e-bike from an electric car plug?
[Trent M. Wyatt]’s CPUVolt library provides a fast way to measure voltage using no external components, and no I/O pin. It only applies to certain microcontrollers, but he provides example Arduino code showing how handy this can be for battery-powered projects.
The usual way to measure VCC is simple, but has shortcomings.
The classical way to measure a system’s voltage is to connect one of your MCU’s ADC pins to a voltage divider made from a couple resistors. A simple calculation yields a reading of the system’s voltage, but this approach has two disadvantages: one is that it constantly consumes power, and the other is that it ties up a pin that you might want to use for something else.
There are ways to mitigate these issues, but it would be best to avoid them entirely. Microchip application note 2447 describes a method of doing exactly that, and that’s precisely what [Trent]’s Arduino library implements.
What happens in this method is one selects Vbg (a fixed internal voltage reference that is temperature-independent) as Vin, and selects Vcc as the ADC’s voltage reference. This is essentially backwards from how the ADC is normally used, but it requires no external hookup and is only a bit of calculation away from determining Vcc in millivolts. There is some non-linearity in the results, but for the purposes of measuring battery power in a system or deciding when to send a “low battery” signal, it’s an attractive solution.
Being an Arduino library, CPUVolt makes this idea very easy to use, but the concept and method is actually something we have seen before. If you’re interested in the low-level details, then check out our earlier coverage which goes into some detail on exactly what is going on, using an ATtiny84.
