Meter clock: keeping “current” time. Read more about the clock:
I’ve seen a few meter clocks in my travels of the web, and I love the idea. A few days ago, I decided that I must have one of my own. Such began the “How to do it” pondering cycle. I had seen builds where the face plate of the meter is replaced. This works, but I wanted to try and find a way to do it without modifying the meter, if possible. After some more ponderation, I came up with what I think is a serviceable idea.
I came across this style of milliamp meter on Amazon. They’re not quite 0-60 mA, but the 0-100 mA (a 0-20mA meter for the hours) is close enough. And they were cheap. So yay.
Part of my requirements were that the clock run off of an Arduino Pro Mini I had lying around, and with minimal additional parts. In order to drive the meters with some degree of precision, I would use the PWM pins to vary the effective voltage across a resistor in series with the meter. This would, by the grace of Ohm’s Law, induce a current that, based on the PWM duty cycle, would be scaled in such a way as to move the needle on the meter to the corresponding hour, minute, or second.
One minor issue came up in the form of the max current the GPIO pins on the ATMega328 chip can source/sink. The pins can source/sink a maximum of 40mA, a bit far from the 60mA needed for the minutes and seconds meters. Enter the transistor.
Using a simple NPN transistor switch circuit, I was able to provide the current for the minute and second meters from the 5V supply. The PWM signals switch the respective transistors on and off, effectively varying the voltage across the resistors in series with the meters.
The resistor between 5V and the meter is actually 2 1/4 watt 100 Ohm resistors in parallel for an effective resistance of 50 Ohms. The two in parallel was necessary as 5V x 0.06A = 0.3W (more than 0.25 that a single 1/4W resistor can handle safely).
Meter clock: keeping “current” time - [Link]
by Avago Technologies:
Analog isolation is still widely used in motor drives, power monitoring, etc whereby applications typically use inexpensive analog voltage control for speed, intensity or other adjustments.
The HCNR201/200 analog optocoupler is commonly added to isolate the analog signal in the front end module of an application circuitry. The optocoupler will be placed between the analog input and the A/D converter to provide isolation of the analog input from the mixed signal ADC and other digital circuitries. The HCNR201/200 is an excellent solution for many of the analog isolation problems.
Fast analog isolation with linear optocouplers - [Link]
Dave teardown 3 classic analog multimeters:
EEVblog #634 – Analog Multimeter Teardowns - [Link]
w2aew @ youtube.com writes:
This video describes and demonstrates a fun little circuit that is designed to create a automatically switching, dual-range analog voltmeter which is intended to be built into a variable power supply. By using two ranges, it permits accurately setting a low voltage such as 3.3 or 5V, as well as accurately setting a higher voltage like 24V. Setting a low voltage using a high voltage meter is not very precise, hence the reason I put this together. The circuit is demonstrated, and the schematic is reviewed to describe the operation.
Of course, there are many ways this can be done – this is just one example. It uses one of my favorite little analog ICs, the LM10 op amp and reference. The LM10 (designed by the legendary Bob Widlar) is used as a voltage reference and comparator with hysteresis. A zener diode is used as a shunt regulator. There’s an indicator LED to show when the meter is in the high range, and a 2N7000 enhancement mode n-channel MOSFET is used to change the resistors associated with the analog meter.
Auto-ranging Analog Voltmeter for a variable power supply - [Link]
Analog Devices, Inc. (ADI) released a new version of its popular ADIsimRF design tool:
The free design tool is the software accompaniment to ADI’s complete portfolio of RF-to-digital functional blocks, allowing engineers to model RF signal chains using devices from across ADI’s RF IC and data converter portfolio. ADIsimRF Version 1.7 adds a number of new device models along with enhanced support for inter-stage mismatch calculations. The design tool provides calculations for the most important parameters within an RF signal chain, including cascaded gain, noise figure, IP3, P1dB, and total power consumption. The ADIsimRF design tool contains embedded data from many of ADI’s RF ICs and data converters, which designers can easily access using pull-down menus to assist in component selection.
Analog Devices releases free version of RF design tool - [Link]
The Digilent Analog Discovery™ design kit, developed in conjunction with Analog Devices Inc., is the first in a new line of all-in-one analog design kits that will enable engineering students to quickly and easily experiment with advanced technologies and build and test real-world, functional analog design circuits anytime, anywhere – right on their PCs. For the price of a textbook, students can purchase a low-cost analog hardware development platform and components, with access to downloadable teaching materials, reference designs and lab projects to design and implement analog circuits as a supplement to their core engineering curriculum.
Analog Discovery – Portable Analog Design Kit - [Link]
I’d really like to know how to “”convert”” an analog value to a digital one. In a word : I have an Arduino, a photoresistor, with a pull-down resistor. I want to know if the light is above or below a given threshold.
I know how to read the value with analogRead(photoResPin), and compare it to my threshold (in code), but I’d like to do that without software (only using digitalRead), handling that threshold in hardware.
Can you help me ?
I guess I can use a transistor, but don’t know how to “”precisely”” set the threshold (by changing the pull-down resistor value ?).
How can I convert an analog value to a digital one? - [Link]
MeterBasic is a fine program for the hobbyist who wants to generate a simple scale on occasion. MeterBasic is based on a subset of the features found in Meter. It requires no key and has no time or usage limitations. To provide an incentive to upgrade from MeterBasic to Meter, many of the features found in Meter are absent.
MeterBasic – Software for drawing analog panel meter scales - [Link]
Here is a simple programmable load. It’s basically a constant current sink that is controlled through a pot. The current is sunk through a high power FET which needs to be cooled to function properly – [via]
Here’s a link to a *really* simple linear constant current sink i put together
This design is about as simple as it gets. . .multi-turn pot controlled and readout done by a voltmeter:) The good news is that it works quite well for moderate loads. It was put together to regulate current flowing through a copper electroplating tank. Due to the monstrous Pentium II (or maybe III?) heat sink, it isn’t noticeably warm when eating 9A of current.
Simple analog programmable load - [Link]
USB Input / Output Board is a quick little development board which replace parallel port . USB IO Board is compatible with Windows computers on HID class which means direct plug like USB mouse or keyboard . When attached to Windows IO board will show up as Found new hardware “Microembeded USB IO” and get installed automatically. You can control 16 individual microcontroller I/O pins by click of a button or entering the hex value of the two 8 bit ports. USB Input / Output Board is self-powered by USB port and can provide up to 500mA for electronic projects. USB IO Board is breadboard compatible. Simply solder included 8-PIN headers on PCB and the board can be plugged into a breadboard for quick prototyping.
PIC 18F4550 USB IO (Input / Output) Board with Analog - [Link]