Having built a small, portable 10.000V reference using the Analog Devices AD587 reference chip, now is a good time to evaluate its performance with a bunch of multimeters.
However, I have a feeling that the AD587 with its 10.000V ±5mV @25ºC is going to be the better performer than some of the multimeters being tested. In today’s performance shootout, ranked in order of their pedigree we have:
Last week I had to have a huge tidy-up of my workspace, things were getting out of control. Finished projects, half completed projects, tools, test wires, components and general junk were just piling up. It was becoming unworkable – things were getting lost, projects forgotten and enjoyment was fading.
Whilst watching YouTube (to avoid the inevitable task of cleaning up), one of those YouTube “Recommended” videos popped up with Adam Savage talking about his workshop. Anyway, in typical Adam Savage fashion, he said a few one-liners. One of them being, “Drawers are where things go to die”, 0:58. I had a laugh at this, thought nothing of it, watched some of his video about his tool stand and stopped watching after about 3 minutes because the whole video is about a tool rack.
Following on from a previous post discussing the Analog Devices AD587 precision 10.000V voltage reference, I built a portable device to utilise the chip.
Some requirements of the project were:
10.000V ±5mV output
Battery operated device
Visual, low battery indication
Small, aluminium housing
Clear front panel
Low cost (under $50), readily available components
A low battery indication was a desired feature to prevent the device being used in an important test and the battery level drops low and compromises the AD587’s performance. A simple green LED will suffice. Output performance of 10.000V (± 5mV) couldn’t be compromised so there is no protection to prevent high current draw from the chip, I’ll just have to be sensible.
Voltage references are a humble piece of hardware, their sole function is to provide a stable, known voltage. This constant, known value of voltage can then be used as a reference for ADCs and DACs as well as provide a precision current source.
This model of chip has an output value of 10.000V ± 5mV (that is, an output value of 9.995V to 10.005V) straight out of the factory. A voltage drift of 10ppm/°C at 25°C meaning that the output voltage will drift by 10μV for each 1°C the chip is exposed to. Additionally, the chip has a voltage trim input, so if you have access to a precision voltmeter, the chip’s output value can be adjusted even closer to 10.000V.
Hey folks, sorry for the long wait between drinks, a few things have been going on – holiday, work, demolishing a leaking bathroom.
Anyway, after years of telling myself to get a function generator and watching eBay for quite a few months, I finally took the plunge and bought one. A broken one. Yes, I bought a broken function generator from eBay.
Sad news from the USA that a fellow Maker, Ahmed, was falsely accused of using his skills for evil. The young inventor had re-purposed a clock and built it into a case with a custom power supply and this was mistaken for a “B-word”.
So, I went looking through some old stuff and quickly found this incriminating photo. The energy-meter hack has everything you need to be accused of making a “B-word”; a digital display, obscure looking device that connects to a computer, electricity and colourful wires.
Following his arrest, Ahmed did an interview with a local news station. Behind him during the interview was his room of electronics, I’ve got one of those too.
Following on from a recent teardown of a low cost appliance energy meter, I’ve done a bit more hacking of the device. As you may recall, I identified that one of the pins on the meter’s chip (EOUT) output a train of pulses proportional to the energy consumed. Some tests with a multimeter seemed to confirm this because the average voltage of EOUT changed with the appliance wattage.
I was hesitant to connect my logic analyser to the meter to measure the EOUT pin because of potential differences in voltage levels. To resolve, this I quickly whipped up a small board with a 4N25 opto-isolator to provide some voltage isolation between the internals of the energy meter and my logic analyser.
Again, I will repeat the obligatory warnings prevail. Do not:
Attempt or copy any of this if you do not fully understand or appreciate the hazards of mains power
Open the meter whilst connected to mains power
Perform any measurements whilst the meter’s case is open
Connect another mains powered device to measure the chip. The energy meter’s power supply is not isolated from active, neutral or earth.
The circuitry that allows for isolation of voltage levels is based around a 4N25 opto-isolator. An opto-isolator allows for a signal to be transferred using light, this provides an airgap which provides electrical isolation.
New Scientist recently detailed the construction materials for the simplest flex sensor I’ve ever heard of – a graphite pencil and a piece of paper. It is obvious when you think about it, but as New Scientist details in in their article Pencil lines as sensors, 21st March 2015 (No 3013) edition,
“MacGyver would be proud. Drawing a rectangle on a piece of paper with an ordinary pencil can create a sensor.”
Probably about 12 years ago, I recovered the imaging sensor from an A4 flatbed scanner that had become obsolete. (I think its obsolescence was due to it having a parallel port interface and my family’s new computer didn’t have a parallel port) Apart from it not being able to communicate with a new computer, it still worked fine sadly. Fortunately, there were several useful components that I recovered from it including a stepper motor, v-belts and pulleys, CCFL light and the CCD.
Well, after all that time saying that one day I’ll get the CCD to work, the time has come.