Recharge a 9V NiMh battery with a Solar Panel / Constant Current Generator LM317LZ

 
If you enjoyed the previous post solar-powered Arduino board, you should keep reading this one as well to improve your solar power generator. In fact, with that setup the 9V battery would decay too soon: A NiMh (Nichel – metal hydroxide) battery must be recharged with a constant current generator, a solar panel alone is not.

In order to do so, we can assemble a quite simple circuit using the following components:

    LM317M or LM317LZ
    A 200Ohm trimmer
    10Ohm resistance
    A LED to check if the current is actually flowing

The core of this circuit is the integrated three-terminal adjustable linear voltage regulator LM317. The ‘adj’ pin is a control terminal that is used to adjust the output current. So, the trick is to use a variable resistor (in our case, a trimmer with a small resistance put in front of it) to set the current at a definite value.

With an input DC voltage of max 24V, and the resistances shown in the diagram, one can obtain an output current of:

I_out = 1.2/(10 + R_trim) [A]

This current must be less than 1/10 of the battery output, e.g. for a 750mAh battery the output current must be less than 75mA. As usual, it is customary to insert a capacitor (100uF should be ok) in parallel at the input node to smooth out fast-varying voltages.

60kHz PIC Function Generator - LF353

  This project is based on the Function Generator described on Mondo Technology web site. I just did very slight changes and fixed some obvious typos in schematic. The code is rewritten for the Microchip MPLAB IDE syntax.

    Device features

        Frequency range: 11Hz – 60KHz
        Digital frequency adjustment with 3 different steps
        Signal forms: sine, triangle, square, pulses, burst, sweep, noise
        Output range: ±15V for sine and triangle, 0-5V for others
        Sync output for pulses

    The device is powered from 12VAC which provides a sufficiently high (over 18V) DC voltage needed for a normal operation of 78L15 and 79L15. The 12V power supplies are replaced with 15V ones. This is done in order to LF353 Op-amp could output the full range of signals to a 1K load. By using a ±12V supply this resistor must be at least 3K.
 

Power Pulse Generator THE LM150/LM250/LM350

Power Pulse Generator THE LM150/LM250/LM350 is an adjustable voltage regulator capable of delivering from 1.2 to 33 volts at a maximum current of 3 amperes. Normally this chip is used in both fixed and adjustable power supplies, voltage regulators and voltage references. Since I'm always looking for a new way to obtain high-current pulses for flashing lamps and driving motors, motors, I have recently been experimenting with ways to switch the output of the LM350T on and off. Since the output voltage of this chip is fully adjustable, a circuit which switches its output on and off provides a variable- amplitude power pulse generator. Before looking at an LM350T power pulse generator, let's first examine the operating characteristics of this versatile chip. Figure 2-42 shows the pin diagrams for both the TO-220 packaged LM350T and the TO-3 versions of the LM150/LM250//LM350. The chip requires a minimum of external components.