Probing mains powered schematics is hard. Most oscilloscopes are earth referenced, so connecting ground probe to random spot of mains connected device will make a small explosion. Also there is the risk of electric shock by touching wrong part of the schematic while being in contact with something grounded like a desktop computer case
To combat these dangers I built an isolator box. I took an 1:1 transformer rated for 230 VAC 50 Hz mains voltage used in Europe. With 0.76 A current output capability it gives me ~170 W to play with. To make it even more useful I added a second output that goes through a diode bridge and has bunch of filter capacitors. This gives me rectified DC voltage to use, since most schematics rectify it anyway.
In this post we introduce simple and flexible, regulated low voltage power supply unit. This power supply has provision for 4 outputs such as 1.5V, 1.8V, 2.5V and 3.3V. We mainly build this low voltage power supply unit to test (and power-up) low voltage MCUs, CPLDs and radio receivers. For this power supply we choose 1.8V, 2.5V and 3.3V to get it compatible with most of the LVTTL/LVCMOS devices. Other than that, we include 1.5V because there are several analog ICs are available for that voltage level.
This power supply unit is based on LM1117/AMS1117 voltage regulator series and for this design we use AMS1117-1.5, AMS111-1.8, AMS1117-2.5 and AMS1117-3.3 fixed voltage regulators. Except to above regulators this board can be use with AMS1117-2.85 and AMS1117-5.0 regulators.
Sometimes you need to check one circuit and test some of its nodes. Usually a tester in voltage mode is a good solution, but it has a pair of problems. First, it measures about zero both when the node is driven at zero volts and when the node is floating (not driven at all). Second, it gives the information on the tester display, so you need to take the view from the circuit to the tester to check the voltage.
The proposed circuit somewhat qualifies as a logic probe. It should give no indication when the node is not being driven and it should give a different indication when the node is driven at high or a low voltage.
A lot of logic probes are not self powered. They rely on the circuit supply to operate. In my case I would like the probe to be usable also a as a continuity tester. If we set ground in one point of the circuit and we probe another point, the continuity can be detected between both points because a low level will be driven even if the circuit is not powered at all.
This is part three of a series about building a active differential oscilloscope probe. Part 1 covered why I wanted a differential probe and the design of it. Part 2 covered actually building the the probe. The probe had much lower bandwidth than I had hoped for but it was still useful.
Here’s a scratch-built 28.8MHz TCXO capable of +-1ppm stability from 0C-55C; best of all, it’s not only easy to build, but is designed entirely from readily available and inexpensive components. For improved temperature stability, the main oscillator can even be replaced with one of many commercially available TCXOs!
Ken Shirriff writes, “What’s inside a counterfeit Macbook charger? After my Macbook charger teardown, a reader sent me a charger he suspected was counterfeit. From the outside, this charger is almost a perfect match for an Apple charger, but disassembling the charger shows that it is very different on the inside. It has a much simpler design that lacks quality features of the genuine charger, and has major safety defects.”
Ashish Derhgawen built a coherer-based receiver with a simple decoherer mechanism, and connected it to a Beaglebone to decode the received signals:
In my last post, I described how I made a spark-gap transmitter and receiver. For the transmitter, I used a car’s ignition coil to produce high voltage sparks, and for the receiver, I used a coherer to detect the transmissions. A coherer is a simple device – it consists of iron filings between two electrodes. Normally the filings have very high electrical resistance (tens of megaohms), but when the coherer detects electromagnetic waves, its resistance drops to about 10-20 ohms.
The Atmel SAM D series of 32-bit microcontrollers includes several devices, each with a long list of features at great prices. Perhaps the best known of the series in the maker community is the SAM D21 due to its use on the Arduino Zero. However, there are several other devices in the product line that are worth taking a look at. The smallest of the bunch is the SAM D09 that comes in a 14-pin SOIC package. The 14SOIC package is one of my favorites. It is easy to solder, easy to break out on a PCB, and takes up little board space. I decided to order some SAM D09C chips and design a small development board in order to learn more about the capabilities of the device.
This application note from OSRAM describes the use of the SFH 4780S in iris recognition (iris scanning) as illumination module. Link here (PDF)
Personal authentication is becoming a key requirement for various electronic devices. Besides of the pin number, today most systems are based on so called biometric “properties”. Biometrics can include fingerprints, facial features, retina, iris, voice, fingerprint, palmprints, vein structures, handwritten signatures and hand geometry. All these biometrics have various pros and cons. However, only iris recognition claims to be a ‘hard-to-spoof’ system in combination with an ultra-low false acceptance rate (i.e. one in a million). Additionally, it also features greater speed, simplicity and accuracy compared to other biometric systems. The traits of iris recognition systems rely on the unique patterns of the human iris which are used to identify or verify the identity of an individual.
This application note from OSRAM describes the possible hazards of infrared LEDs (IREDs) used for lamp applications with respect to the IEC-62471 standard and how to classify IREDs according to different risk groups. Link here (PDF)
As the radiated optical power of light emitting diodes (LEDs) has increased in recent years, the issue of eye safety has received an ever-increasing amount of attention. Within this context there has been much discussion about the right safety standard either the laser standard IEC-60825 or the lamp safety standard IEC-62471 to apply to the classification of LEDs. Before mid 2006 all LED applications were covered by the IEC-60825. Today most of the LED applications are covered by the lamp standard. Other than lasers, lamps are only generally defined in this standard as sources made to produce optical radiation. Lamp devices may also contain optical components like lenses or reflectors. Examples are lensed LEDs or reflector type lamps which may include lens covers as well. The status quo is, that for different applications of LEDs, like data transmission or irradiation of objects, different standards have to be used: data transmission IEC-60825 & lamp applications IEC-62471. Both safety standards do not cover general exposure scenarios and are not legally binding.