Abel Raynus writes:
Rechargeable NiCd (nickel-cadmium) cells are widely used in consumer devices because of their high energy density, long life, and small self-discharge rate. As a part of one project, I needed to design a reliable and inexpensive charger for a battery pack containing two NiCd AA-size 1200-mAh cells. In the process of the charger design, I needed to solve two main problems: first, setting a proper charge-current value, and second, stopping the charging process when the cell is full to avoid overcharging. This Design Idea describes a way to overcome both problems.
Charge a nickel-cadmium cell reliably and inexpensively - [Link]
janw @ instructables.com writes:
A few months ago, I saw an instructable by fjordcarver on how to build a coloursensor with an RGB led and an LDR. It inspired me to try whether I could improve his design.
Here are the things that I wanted:
The sensor should have as few pins as possible.
It should work as a stand-alone device. All calculations should be done on the device.
It should have a triggered mode and a continuous mode.
All parameters should be programmable.
Calibration parameters should be stored in the EEPROM of the microcontroller.
Firmware updates should be made possible
And finally: size does matter ⇒ The smaller the better.
I did choose an smd attiny85 as the brain of the sensor. It has a small footprint but a large enough flash for the calculations. It also has just enough pins for the project (all eight pins are used).instructables.com
Build your own (at)tiny colour sensor - [Link]
by Abhijeet Deshpande:
Properly maintained rechargeable batteries can provide good service and long life. Maintenance involves regular monitoring of battery voltage. The circuit in Figure 1 works in most rechargeable batteries. It comprises a reference LED, LEDREF, which operates at a constant current of 1 mA and provides reference light of constant intensity regardless of battery voltage. It accomplishes this task by connecting resistor R1 in series with the diode. Therefore, even if the battery voltage changes from a charged state to a discharged state, the change in current is only 10%. Thus, the intensity of LEDREF remains constant for a battery state from a fully charged state to a fully discharged state.
Simple battery-status indicator uses two LEDs - [Link]
Aurora 48 is a compact and thin profile full-color LED sequencer. It’s built entirely with surface mount components, so the profile is nice and clean.
Aurora 48 – 48 RGB LED Sequencer - [Link]
Harrymatic @ instructables.com writes:
I am in the process of designing a function generator and I needed a frequency counter to check it against. This project uses a minimal number of components for a very economical and compact design. A bare-bones Arduino clone is at the heart of this project and the measured frequency is shown on an LCD display. The maximum frequency that this can measure is about 8 MHz (at a 50% duty cycle). Despite the fact that this counts the frequency on one of the digital pins, I have found that it will quite happily measure sine and triangle waves providing that they have a suitable amplitude.
8MHz Frequency Counter - [Link]
by Publitek European Editors
This article looks at the options for getting started with a GPS design for industrial applications, from the transceivers to modules and the evaluation boards available, as well as the antenna issues to consider. It looks at how modules from suppliers such as Antenova and NXP Semiconductors can be used, extending to single chip implementations from Maxim and Skyworks.
Navigation and positioning are becoming increasingly popular functions in many devices, from dedicated satellite navigation handsets to integration in mobile phones and automobiles. They are now appearing in digital cameras and even used for tracking high value assets, making the integration of navigation technology an important design element. However, this brings together digital processing, software, analog and RF design expertise that may not be common within one company.
Getting Started with GPS - [Link]
Mizchief100 @ instructables.com writes:
I love robots. Normally the ones I build are quite large and wouldn’t fit in your pocket, but for a change of pace I decided I would try something small and fun! This robot is exactly that, and in fact fits inside of an altoids tin. It is inexpensive, versatile (so many different sensors can be used), and extremely entertaining. Check it out in action below! (Unfortunately I played with mine so much before I took any video I had used up my coin cell batteries and one motor started having issues, so I’m driving it with a 9V in the video)
Tiny Altoid Tin Robot With Personality - [Link]
Here’s a handy USB Breakout Board that makes measuring USB 2.0 current draw, data, or whatever, a snap.
USB Breakout Board - [Link]
by Fran Hoffart:
A circuit that properly charges sealed lead-acid batteries ensures long, trouble-free service. Fig 1 is one such circuit; it provides the correct temperature-compensated charge voltage for batteries having from one to as many as 12 cells, regardless of the number of cells being charged.
The Fig 1 circuit furnishes an initial charging voltage of 2.5V per cell at 25°C to rapidly charge a battery. The charging current decreases as the battery charges, and when the current drops to 180 mA, the charging circuit reduces the output voltage to 2.35V per cell, floating the battery in a fully charged state. This lower voltage prevents the battery from overcharging, which would shorten its life.
Charger extends lead-acid-battery life – [Link]
By Steven Keeping
Switching DC/DC voltage converters are popular because they provide efficient power conversion that can exceed 90 percent. That is an advantage both when input power is at a premium and when it is difficult to get the heat out (common challenges for engineers designing compact portable products).
With key power component manufacturers offering products that appear virtually identical on the specification sheet, it is tempting for an engineer to just pick a switching converter with the highest peak efficiency from a shortlist that meets their product’s general requirements. However, that would be a mistake because apparently identical converters can offer markedly different performance.
This article considers the major implications for power dissipation and associated heat rise that just a few percentage points difference in efficiency can make. The article then leads on to discuss how, depending on the load pattern, a converter with lower peak efficiency, but a flatter efficiency curve, could well be the better choice for a particular application.
Selecting the Right Voltage Converter Is Not Just About Peak Efficiency - [Link]