electronic schematic info

Low Power LED Voltmeter by LM3914

2009-01-15T17:54:00.003+07:00

This is a low power voltmeter circuit that can be used with alternative energy systems that run on 12 and 24 volt batteries. The voltmeter is an expanded scale type that indicates small voltage steps over the 10 to 16 volt range for 12 volt batteries and over the 22 to 32 volt range for 24 volt batteries. Power consumption can be as low as 14mw when operated from 12V and 160mw when operated from 24V. It is possible to set the meter to read equal steps across a variety of upper and lower voltages. The meter saves power by operating in a low duty-cycle blinking mode where the LED indicators are only on and consuming power briefly during a repeating 2 second cycle. The circuit may be switched to a high power mode where the active LED stays on at all times.

Different colored LEDs may be used for the voltage level indicators, this allows the battery state to be read in the dark. With the new blue LEDs, it is possible to have a nice looking rainbow of colors using two each of red, amber, yellow, green, and blue LEDs. The circuit will also work with inexpensive and common red LEDs. If the circuit is to be used in sunlight, ultra-bright LEDs should be used, although even those may be hard to read without some kind of sun shield.

Typical uses include the monitoring of portable battery operated systems and indoor wall mounted home power system charge indicators. The cost of the parts for the circuit is around $25.00 (US) and the parts are commonly available, except for the optional blue LEDs. If blue LEDS are used, expect to pay a premium for them, they cost several dollars each, compared to around 15 cents for the other colors. The blue LEDs do look nice in any case.

The circuit may be built with either the CMOS ICM7555 timer or the more common bipolar 555 timer. The 7555 timer will provide much more efficient operation and should be used for systems with small batteries. The volt meter works nicely with the solar charge controller and low voltage disconnect circuits described in the home-brew section of Home Power #60 and #63.

Logic Probe w/Pulse Injector

2008-08-21T18:14:00.002+07:00

This is an useful and easy-to-build Logic Probe with Pulse injector. A schematic of a “digital version” is included.

Here is the schematic of my Logic Probe with Pulse Inyection:

Logic Probe with pulse inyection

If you work with digital circuits, TTL or CMOS, you may know sometimes is not easy to diagnose a problem or know the reason of an unexpected behavior in the circuit. That is the function of the Logic probe, It helps to monitor the signal on every connection. As the pulse injection is included, it also can help to send some pulses to the circuit. This is a perfect tool when developing circuits.

I built this one on 1989 when I was at the school learning about digital electronics. I saw one that does the same thing, monitors and injects pulses, with a cost of a few hundred dollars. I built mine for only $7 USD. I don’t have any picture because that was more than 15 years ago, but I remember clearly that I used a toothbrush case. My friends were astonished how perfectly it worked.

How this works:

The power for the logic probe is taken from the circuit to monitor. As a CMOS is used, it works with 3V to 15 Volts. The tip is connected to the point in the circuit that needs to be monitored. To inject pulses, just close the switch. Pulse injection is used when working with latches, flip-flops, etc.

Here is another version of the same circuit that shows when the signal is “1″, “0″ or “P”:

Schematic Digital Logic Probe

I don’t use a logic probe anymore because I have enough computers to use simulators, however, soon I will start working with digital circuits and I will build my own Logic probe with pulse injector. By the way, this logic probe does NOT recognize the third state or hi-z.

LEAD ACID BATTERY CHARGER

2008-08-21T17:46:00.002+07:00

DESCRIPTION

(A) BASIC TRANSFORMER
Voltage is transformed by the transformer turns ratio N2/N1. For instance if 20VAC secondary voltage is required with 120VAC input, a 6:1 ratio would be needed. When full load current is drawn from the secondary winding, the voltage may drop from 5 to 25%, this effect is known as voltage regulation. Addition of a thermal fuse to the primary circuit insures safe operation in the event of an output short circuit or overload.

(B) UNREGULATED POWER SUPPLY
Capacitor C1 will charge up to 1.414 times the RMS secondary voltage minus the diode drop. Applying a loading current will cause the output voltage to drop by about 20 to 30%, the percentage drop is referred to as the voltage regulation. The circuit shown uses a center-tapped winding and 2 diodes, a non- center-tapped winding with 4 diodes is probably the most common configuration.

(C) LINEAR MODE REGULATED POWER SUPPLY
Unregulated DC power supplied from C1 powers the linear regulator. The regulator will precisely control the output voltage for critical circuit applications. Capacitor C2 is used to prevent oscillations in the regulator, it also improves regulator transient response characteristics. When the voltage at C1 minus the minimum regulator drop falls below the output voltage rating, the regulator is at the low-line point.

(D) SWITCHMODE REGULATED POWER SUPPLY
This type of regulator utilizes hi frequency switching techniques to minimize transformer size and maximize efficiency. Various converter topologies are the forward, boost, flyback and resonant. The flyback converter shown at left uses PWM (Pulse Width Modulation) circuitry to regulate the output. By modulating the switch at a fixed frequency with a given duty cycle the output voltage can be expressed as:
Vout= Vin (D.C./1-D.C.) x (N2/N1)
Where D.C.=Duty Cycle
Additional circuits are needed in order to comply with EMC Requirements.

(E) NICAD BATTERY CHARGER
The most common charging technique is the C/10 charger. C is the Amp/HR capacity of the battery. This type of charger requires approximately 12 to 14 hours to replenish a fully depleted battery. The current limiter can either be a resistive element or an electronic circuit. An indicating LED is useful for providing visual means to show charging is taking place.

(F) LEAD ACID BATTERY CHARGER
Voltage limited charging techniques are essential to extend battery life. At room temperatures lead acid cells require 2.3V per cell to stay at 100% charge. Voltage tolerance of the charging circuit should be kept to +/-1% by the use of voltage trimming. Recharge times of 3 to 5 hours can be realized with standard lead acid cells.

12V Lead-Acid Battery Monitor

2008-08-21T16:53:00.002+07:00

This simple circuit makes it posible to monitor the charging process to a higher level. Final adjustsments are simple and the only thing needed is a digital voltmeter for the necessary accuracy. Connect an input voltage of 12.65 volt between the positive and negative poles and adjust the 10K trimmer potentiometer until Led 10 lights up. Lower the voltage and in sequence all other Led's will light up. Check that Led 1 lights up at approximately 11.89 volts.

At 12.65 volt and higher the battery is fully charged, and at 11.89 is considered 'empty'. The green Led's indicate that the battery capacity is more than 50%, the yellow Led's indicate a capacity of 30% - 50% and the red Led's less that 30%. This circuit, with the components shown, uses less than 10mA. Ofcourse you can adapt this circuit to your own needs by making small modifications. The circuits above is set for 'DOT' mode, meaning only one Led at a time will be lit. If you wish to use the 'BAR' mode, then connect pin 9 to ground, but obviously with increased current consumption. The LED brightness can be adjusted up- or down by choosing a different value for the 4K7 resistor connected at pin 6/7 You can also change the to monitoring voltage level. For example, let's say you wanted to change to 10 - 13 volt, you connect 13volt to the input (+ and -) and adjust the 10K potentiometer until Led 10 lights up. Change temporarily the resistors at pin 4 with a 200 Kilo-ohm potentiometer and reconnect a voltage from 10 Volt to the input. Now, re-adjust the 200K potentiometer until Led 1 lights up. When you are satisfied with the adjustment, feel free to exchange the 200K potentiometer with resistors again.(after measuring the resistance from the pot, obviously).

The diode 1N4007 was included to protect the circuit from a wrong polarity connection. It is however strongly recommended to connect the monitor directly to the battery, in principle a connection to the cigarrette lighter would suffice but for reasons unknown at this time the voltage at that point is 0.2 volt lower than the voltage measured directly on the battery. Could be some residual resistance caused by ignition switch and path through the fuse?

Frequency Counter with microntroller PIC16F84A

2008-08-12T17:22:00.004+07:00

This is 1GHz frequency counter with 100KHz resolution. Meter is built in around PIC16F84A microcontroller and SAB6456 / U813BS prescaller.

PIC Temperature Meter with Thermoster

2008-08-12T17:10:00.002+07:00

This is our upcoming project that is similar to PIC dual temperature meter but with the thermostat option built-in. Besides displaying customized temperature readings in Celsius and/or Fahrenheit degrees it will turn on heater if the temperature drops below specified temperature or it can be set to turn on the fan or air conditioning system if the temperature reaches above specified temperature that is set by UP / DOWN buttons. Thermostat can display both Celsius and Fahrenheit values (together or individually) and is capable of measuring temperatures from -55 to 125 degrees Celsius (-67 to 257 degrees Fahrenheit)

Presented PIC temperature meter with thermostat uses very exciting DS1820 1-Wire digital temperature sensor. Unlike regular sensors where temperature readings are passed as varying voltage, DS1820 passes temperature information in a digital format as data. This brings many new possibilities and enables to pass temperature information over much longer distances just over a two wire cable.

Stay tuned for full details on this project.

input 0-70V PIC Voltmeter

2008-08-12T16:55:00.003+07:00

This is a sneak preview of upcoming PIC voltmeter project. You may use this PIC voltmeter for your power supply, as a battery meter for car, RC cars, RC helicopters, to monitor voltages in your computer or it could be used as a small portable voltmeter.

This is extremely simple to build PIC Temperature meter that allows to measure temperature in two different locations at the same time. Meter can display both Celsius and Fahrenheit values (together or individually) and is capable of measuring temperatures from -55 to 125 degrees Celsius (-67 to 257 degrees Fahrenheit). Never before such a useful and powerful circuit could be built with so little components and yet provide endless possibilities. This is all possible thanks to the use of PIC16F628 microcontroller and 2x16 character LCD display that act like a small computer which can be customizable thanks to upgradeable hex firmware.

Presented PIC temperature meter uses two very exciting DS18S20 1-Wire digital temperature sensors. Unlike regular sensors where temperature readings are passed as varying voltage, DS18S20 passes temperature information in a digital format as data. This brings many new possibilities and enables to pass temperature information over much longer distances just over a two wire cable

Led display digital Voltmeter

2008-08-11T17:26:00.002+07:00

This is an easy to build, but nevertheless very accurate and useful digital voltmeter. It has been designed as a panel meter and can be used in DC power supplies or anywhere else it is necessary to have an accurate indication of the voltage present. The circuit employs the ADC (Analogue to Digital Converter) I.C. CL7107 made by INTERSIL. This IC incorporates in a 40 pin case all the circuitry necessary to convert an analogue signal to digital and can drive a series of four seven segment LED displays directly. The circuits built into the IC are an analogue to digital converter, a comparator, a clock, a decoder and a seven segment LED display driver. The circuit as it is described here can display any DC voltage in the range of 0-1999 Volts.