Spacewrench over at Dorkbotpdx published a new build, a Power Playground project:
It’s a PMOS/NMOS H-Bridge with FETs that can handle 3 amps or so, plus a SPI current sensor, some switches & a rotary encoder (not stuffed yet), and a 7-segment display, all controlled by a Teensy-3.1 running FreeRTOS.
I made this because I’m always running into battery, power, inductor and transformer issues I don’t have any experience with. The idea is to use the H-bridge configuration and current sensors to experiment with moderate-current PWM, motor control, power-line synchronization, battery charging and discharging, etc.
Power playground project - [Link]
by Vladimir Rentyuk @ edn.com
Suppose that you need to test a 1.5V, AA-size alkaline battery. You can apply a short circuit and measure current, or you can measure open-circuit voltage, but neither method properly tests the battery. A suitable test current of approximately 250 mA gives you a more reasonable test. You can use a 6Ω resistive load at 1.5V, which produces an output voltage of 1.46V at an ambient temperature of 25°C if the battery is in excellent condition. A poor battery might produce less than 1.2V. Given the load, the output current at 1.2V will be 200 mA instead of 250 mA. The battery will have just 80% of a full load current. Instead, you can use the circuit in Figure 1 to produce a constant-current load.
Circuit provides constant-current load for testing batteries - [Link]
by DIY Hacks and How Tos @ instructables.com:
A “Joule Thief” is a simple voltage booster circuit. It can increase the voltage of power source by changing the constant low voltage signal into a series of rapid pulses at a higher voltage. You most commonly see this kind of circuit used to power LEDs with a “dead” battery. But there are many more potential applications for this kind of circuit.
In this project, I am going to show you how you can use a Joule Thief to charge batteries with low voltage power sources. Because the Joule Thief is able to boost the voltage of a signal, you are able to charge a battery with a power source whose output voltage is actually lower than the battery itself.
This lets you take advantage of low voltage power sources such as thermoelectric generators, small turbines and individual solar cells.
Joule Thief Low Voltage Battery Charger - [Link]
The LTC®3305 balances up to 4 lead acid batteries connected in series. All voltage monitoring, gate drive, and fault detection circuitry is integrated. The LTC3305 is designed for stand-alone operation and does not require any external control circuitry.
The LTC3305 employs an auxiliary battery or an alternative storage cell to transfer charge to or from each individual battery in the stack. A mode pin provides two operating modes, timer mode and continuous mode. In timer mode, once the balancing operation is completed, the LTC3305 goes into a low power state for a programmed time and then periodically rebalances the batteries. In continuous mode, the balancing operation continues even after the batteries are balanced to their programmed termination voltage.
LTC3305 – Lead Acid Battery Balancer - [Link]
If you´re deciding whether it´s worth to use a backup battery, we bring you a few remarks why to go for it or not.
Lithium battery Xeno Energy with a lifetime of over 10 years and rules for their usage were brought to you in our article „10 years of operation for 1 battery?”. They´re usable as a “main” power source for low power consumption devices and the second main field of their usage is a power supply backup. In contrast to the smallest cells used for PC memories backup (BIOS) for example, the types, which we keep in stock feature capacity of several Ah and they´re also able to provide a relatively decent current. That enables to use such battery also for a real operation of the device (MCU) during the power supply dropout.
Probably the main reason why not to use a backup battery is a doubt about higher production costs of a given device. However, when we look at the sales price in our e-shop, we find, that common PCB types like for example XL-050F AX (LS14250CNA) or XL-060F AX (LS14500CNA) are available for the price of max. 4 Eur/pce. At the same time, using this type of batteries eliminates the need for a battery holder, charging chip, etc.
The newest contribution on the field of PCB lithium batteries in our stock is the type XL-210F/STD 5,5mm, what´s the disc with 33mm diameter and only 6.6mm height, with leads to be soldered to PCB (THT). Low profile enables usage even in slim devices and everywhere, where common cylinder types are not suitable.
Further information will provide you the Xeno short form catalogue as well as detailed datasheets of Xeno batteries. In the Xeno production portfolio can also be found special batteries with a higher pulse capacity and type for extra high temperatures -55 to +130°C.
Backup battery soldered directly to a PCB? - [Link]
by micahmelnyk @ instructables.com:
In short: I developed a portable, battery powered device that sounds an alarm when your bag or purse is moved. Once armed, can only be turned off by your secret code.
The device is built off an Arduino compatible Trinket Pro, using an off-the-shelf project box with PCB.
Bag movement alarm for theft prevention - [Link]
by David Nield @ gizmag.com:
The batteries inside our smartphones and laptops are fighting a losing battle when it comes to keeping these devices juiced up, but researchers from ETH Zurich have discovered a new type of glass material that could make a major difference: vanadate-borate glass. The glass can be used as an electrode material in lithium-ion batteries to almost double the amount of time they last between charges.
A new type of glass could double your smartphone’s battery life - [Link]
Li-Ion/Polymer Shunt battery charger system with low battery disconnect (PDF!) app note from Linear Technology:
The LTC®4071 allows simple charging of Li-Ion/Polymer batteries from very low current, intermittent or continuous charging sources. A near zero current low battery latching disconnect function protects even the lowest capacity batteries from deep discharge and potentially irreparable damage. The 550nA to 50mA operating current makes charging possible from previously unusable sources. With its low operating current the LTC4071 is well suited to charge low capacity Li Ion or thin film batteries in energy harvesting applications. The unique architecture of the LTC4071 allows for an extremely simple battery charger solution, requiring just one external resistor.
Li-Ion/Polymer Shunt battery charger system with low battery disconnect - [Link]
Perhaps the most frequently used rechargeable batteries on the market nowadays – Lithium-Polymer (Li-Po) can be found also in our offer.
From the beginning of electronics, the world searches for an “ideal” rechargeable battery. So far such a battery doesn´t exist (maybe supercapacitors in the future), but Li-Po (Li-Pol) cells are quite near to an ideal in some aspects.
Very low self-discharge (approx. 5% / month), high voltage of a cell (3,7-3,8V average), high energy density and a low weight, considerably stable discharge voltage and a possibility to recharge anytime are one of the main advantages of Li-Po cells. Another benefits are advantageous flat shape, high variability in dimensions and a long lifetime. No wonder, that Li-Po cells have become no. 1 in consumer electronics, hand tools and in many industrial devices.
Perhaps the only drawback of these cells is their lower chemical stability at overcharging (in a corner case ending up with a fire). But that´s the case which is practically eliminated at a common operation with a suitable charging circuit (chip or a charger intended for Li-Po).
Basic principle at usage is not to exceed approx. 4.25V charging voltage and the battery is almost discharged at a voltage below approx. 3.0V (2.75V). On the very end of a discharge cycle, the inner resistance slightly increases, what can cause a slight heating of a battery at higher currents – it is a normal behavior. Charging is usually based on a method constant voltage/ limited current. In principle it´s possible to use the same chargers and charging circuits for Li-Ion as well as Li-Po cells.
At a usual usage and discharging to say 20-80%, Li-Po cells will reward you by a reliable operation and a long lifetime. Flat shape is ideal for various handheld equipment, as well for usage in flat enclosures. In respect to a low self-discharge it´s possible to use Li-Po cells even as a backup energy source.
In our offer can be found several several Li-Po types from company EEMB with a capacity of 130 mAh to 2000 mAh. Exact list of available types and datasheets can be found below this article. Upon request, we´re able to provide you also many other types.
Try the most favorite type of batteries - [Link]
Limpkin wrote this blog article about his tiny NFC Reader with a TRF7970A build, and he will be giving a few of them away:
The main components are:
– the USB-enabled ATMega32U4
– a connector for the NRF24L01
– a Lithium-Ion battery charger
– an NFC transceiver
– a proximity sensor
The main idea of this platform is to read NFC tags while keeping its power consumption low. The microcontroller is communicating with the NFC transceiver so you can use the platform as a standalone device or computer peripheral.
You could therefore control a switch (using the expansion header), send the tag data via RF (using a NRF24L01 you’d connect) or simply have the ATMega32U4 forward the read/write commands sent from your computer. The original idea was to support libnfc.
Tiny NFC reader with a TRF7970A - [Link]