Forth in 7 easy steps
Forth is a simple language, with simple rules and a simple execution model. It’s also self-hosted and interactive - you can type this at the prompt:1 2 + .<cr> What you’ll get as response is this...
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Preparing for serial re-flashing
The STM32F103 µC chips all have a ROM-based boot loader on board. Most chips variants can only be re-flashed via USART1, using the PA9 and PA10 pins, so we will need to connect to that serial port...
View ArticleA new serial tool: vive la Folie!
Working with embdded µC boards involves quite a few steps: apart from the hardware itself, you need to connect to it and figure out how to upload code, of course. But you also think about the...
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Adding the RFM69 module
The last step to create a wireless node is to hook up the RFM radio. Here is what we’re after:There are 4 signals and 2 power pins to connect (more can be added later, for pin...
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The limitations of the ADC
The Analog-to-Digital-Converter (ADC) we all know from Arduinos and other µCs is a marvel of integration and electronics engineering. Able to measure at rates of over a million samples per second...
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Measuring negative voltage
The task to be tackled here is measuring voltage ranging from +N to -N Volt with an ADC input which needs to be kept in the range 0 to 3.3V.There are numerous resources all over the web which solve...
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Op-amps and virtual ground
The voltage-divider-tied-to-3.3V trick allows shifting the level of an input voltage to another range. But there are a few issues with it.The first one is that we still cannot measure anything above...
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Fixing the offset problem
There is still a fairly serious flaw in our little voltmeter setup: its Vin input is not at ground level. It’s connected via Z1 and Z2 to that 2.4V or so virtual ground we just created, and when Vin is...
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Let's measure ± 20V @ 11MΩ
So much for theory and design. Here’s a built-up version of the voltmeter:It was built as add-on for the RF Node Watcher, here’s the side view of this sandwich:Everything was built with through-hole...
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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...
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Op-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 resistancethere is zero current into and out of both V+ and V-if...
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Better 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...
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Water 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...
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And 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...
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A 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...
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Energy 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...
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Powering 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...
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Reading 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...
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A 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...
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Measuring 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 +...
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