Slowed-down by the slew rate
Let’s re-visit the voltage meter for a moment - the actual circuit used in the next test differs in a few resistor values, but it’s still essentially the same as the triple op-amp setup described...
View ArticleOp-amp parameters explained
It can’t be shown often enough - the most elegant building block in electronics: In an ideal op-amp … the V+ and V- inputs have infinite resistance there is zero current into and out of both V+ and V-...
View ArticleBetter speed and sensitivity
First off, let’s find out how that last single op-amp circuit works in practice. The chip used is an LMC6484 quad CMOS op-amp with extremely high input impedance. Since it’s also rail-to-rail on both...
View ArticleWater and electricity don't mix
The hot water tap in the kitchen at JeeLabs is provided by what’s called a “close-in boiler” in the Netherlands: a small 7L electrical boiler, sitting under the kitchen sink and hooked up with two...
View ArticleAnd then the JeeNode stopped
Unfortunately, the USB power supply is not all that got damaged by the water leak: There’s a blueish sludge on the RJ12 jack. Presumably some copper salt caused by humidity and corrosion. This is a...
View ArticleA new design, moving to 32-bit
With one of the two main energy metering nodes out of order, it’s becoming more urgent now to implement a replacement. It would be a shame to break the cycle, after some 8 years of data collection, all...
View ArticleEnergy monitor requirements
The meter cupboard is - as one would expect - the place where lots of energy-related matters come together. Here is the situation as of early 2016 at JeeLabs: Note: that “JeeLabs Energy Monitor” is...
View ArticlePowering from an AC source
Ok, we have a name: “JeeLabs Energy Monitor” - and we have a board to use: the Olimexino-STM32. As mentioned before, that board has a number of convenient features for this project. Then again, any...
View ArticleReading out the pulse counters
Unfortunately, progress on pulse input recognition has been a bit slow - partly due to unrelated “time sinks” - so this will be an overview of some other details of the JeeLabs Energy Monitor. The...
View ArticleA remote console w/ ESP-Link
The ESP-Link is a clever project, which turns an ESP8266 WiFi module into a transparent serial link - sort of a wireless FTDI interface. Thorsten not only created a really powerful software package for...
View ArticleMeasuring AC supply voltage
With the JeeLabs Energy Monitor prototype hooked up in the meter cabinet, it’s now very easy to explore things a bit. One interesting test is to look at the analog signal from the AC power supply +...
View ArticleWhen an input pin isn't one
The article about the ESP-Link ended with what turned out to be an ominous note, in hindsight: There’s still a buglet in this setup: the “reset” word leads to a runaway loop of “Unhandled Interrupt...
View ArticleGreat ADC/DMA performance
For the “JEM” JeeLabs Energy Monitor, we’re going to need to put the ADC on the Olimexino’s STM32F103 to some serious work: the goal is to acquire 4 ADC channels at 25 Khz each, so that we can capture...
View ArticleSome µC speed measurements
Not long ago, Ken Boak very generously donated one of his assembled PCB designs to JeeLabs: This is a break-out board for the STM32F746VG, an ARM Cortex M7 CPU with floating point and a whopping 1 MB...
View ArticleTracking pulses w/ interrupts
There are three pulse counters for measuring power at JeeLabs - one for solar PV production and two for the kitchen stove and the rest, respectively: These generate 2000 pulses per kWh, that’s one...
View ArticleFrequency aliasing in ADCs
This is a pure sine wave, captured by the ADC + DMA code, as described previously: The plot above consists of 800 samples, sampled 40 µs apart, i.e. at 25 kHz - for a total of 32 ms. A quick...
View ArticleSimple variable packet data
Until now, most of the wireless sensor nodes here at JeeLabs have been using a simple “map C/C++ struct as binary” approach as payload format. The advantage of this is that it simplifies the code in C...
View ArticleParsing P1 smart meter info
The smart meter at JeeLabs looks like this: It’s a Landis & Gyr E350, which monitors all power coming into the house and going out (when solar PV production exceeds local consumption). There’s an...
View ArticleThe need for multitasking
With an increasing number of sensing and reporting activities taking place on the JeeLabs Energy Monitor (JEM) prototype, things are starting to become a bit more complicated. How can we deal with such...
View ArticleUsing a buffered serial console
Mecrisp Forth comes with a serial-port command line interface. This makes both tinkering and uploading new code a breeze, but it’s nevertheless a fairly limited setup: no input buffering: if characters...
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