Ultra Low Power LCD Indicator

This circuit serves as an ultra-low power replacement for multiple LED on-off indicators. It also has the advantage of being easy to read in full daylight. With the parts shown, it is possible to display four bits of information.

The display that I used has three digits and 2 decimal points for a total of 23 segments. Different groupings of segments can be used for the four indicators. I chose to use three squares (shown) and the three lower segments together (not shown) for the four indicators. Many other combinations could be used, one possibility would be to hard-wire numbers or letters out of each of the digits. Other LCD displays could also be used for different effects.

A part that doesn't exist as far as I know, but should, is a single pixel LCD indicator (2 wire). An LCD manufacturer could probably make a lot of money with such a part. If such a thing exists, I'd love to hear about it.


Operating Voltage: 3-15V (5V Nominal) DC
Operating Current: 250 microamps to 1 milliamp (400 microamps at 5V)
Operating Frequency: approximately 60 Hz


The 7555 IC (CMOS 555 timer) generates a square wave clock signal at approximately 60 hz. This signal is sent to the LCD backplane and the inputs of the four CMOS 4070 XOR gates. If the other input (ind*) of an XOR gate is low, the gate's output is a square wave that is in phase with the clock signal. If the ind* input is high, the gate's output is out of phase with the clock.

Sending a signal to an LCD segment that is in phase with the backplane signal causes the display to stay blank. Sending an out of phase signal to the LCD segment causes an AC waveform to be applied to the segment which turns it black. Multiple segments are wired in parallel to generate the desired display patterns. The LCD segments require a tiny amount of current to operate, the CMOS gates also take very little power, hence the efficient nature of the circuit. It is necessary to tie the unused segments to the LCD backplane, otherwise they may partially turn on.

If more dislay bits are needed, additional XOR gates can be connected in the same manner. Up to 23 XOR gates could be used to drive the entire display, but a microprocessor and driver software would probably be easier to put together. By generating all of the signals with a microprocessor, all of the driving circuitry can be eliminated.

Other logic families could be used to make this circuit, it should work with a standard 555 timer chip and a 74LS86 XOR gate (different pin out), for example. Some LCDs may not operate at very cold temperatures, an engineer at Lumex said that their components will work from -30C to +75C.


The circuit was built on a standard prototyping plug board. All of the parts can be purchased for under ten dollars.


The four inputs of the CMOS 4070 IC can connect to outputs on a microprocessor, or any other logic output that needs monitoring. The supply voltage of this circuit should be the same as the driving logic's supply voltage.


1X Lumex LCD-S301C31TR 3 digit LCD display (from Digi-Key), or equivalent
1X CMOS 4070 quad XOR Gate, a CMOS 4030 should also work.
1X 7555 CMOS 555 timer chip
2X 100nF capacitor
1X 100uF 25V electrolytic capacitor
1X 10K 1/4W resistor
1X 100K 1/4W resistor
ReadmoreUltra Low Power LCD Indicator

Reset Microprocessor RS-232

Microprocessor RS-232


This circuit allows a remote microprocessor to be reset by a controlling host by sending a break signal over an RS-232 or RS-422 serial line. If the remote machine resets into a simple program loader program, it is possible for the host to halt and restart, or halt and reload/restart the remote machine's program. This is an ideal way to develop software on older EPROM-based systems. Modern EEPROM/NVRAM systems use JTAG interfaces for similar results.

The remote processor runs its target code out of RAM, allowing the code to be updated easily. The circuit is usually used for developing code on a target processor, but it can also be used for permanent applications where the target program lives on a host system's disk. This system was once used to load code into a microprocessor-based satellite receiving system in Hawaii from a host system in Colorado using an Internet-based remote serial communications program.

A program loader for the Z80 CPU is available below. The circuit has also been used with the Motorola 68HC11 EVB and the BUFFALO monitor program. See my Linux Cross Assemblers page for more info.


This circuit detects long duration zero level signals (breaks) on a NRZ (non return to zero) serial data line. Normal serial characters spend a short time in the zero state, and do not cause a reset. Break signals are a exception to this, they hold the line low for an extended period.

The 10K/1N4148 parts keep the 2.2uF capacitor charged up. Low input signals go through the 10K resistor and slowly pull the charge on the 2.2uF capacitor down. High input signals quickly recharge the capacitor through the 1N4148 diode. A break signal lasts long enough to discharge the 2.2uF capacitor to the point where the following gate changes state.

The 1N4148 on the right allows a manual break switch to be used on the target CPU, pressing such a switch does not short out the preceding 74HC14 gate. This circuit could be built with just 2 schmidt trigger non inverting buffers, the 74HC14 was chosen because it is a common part. The parallel inverters are also optional, single inverters work fine.

source : http://www.solorb.com

ReadmoreReset Microprocessor RS-232

Nine Volt Battery Eliminator Circuit

Nine Volt Battery Eliminator Circuit

Effect pedals for electric guitars are typically powered by 9 volt batteries. These batteries cost several bucks each and don't often last very long. Leaving a pedal turned on overnight by accident guarantees a dead battery in the morning. Why spend your precious money on a constant supply of batteries when you can build this easy substitute that won't fade away right in the middle of that killer guitar solo. This device is not limited to use in guitar pedals, it can be used with guitar tuners, radios and other small 9V devices. The circuit can be built to support DC or AC wall warts, the AC version requires a bridge rectifier. I've build many of these out of surplus materials, they make good gifts for guitar players.

If an AC wall wart is used, the low voltage AC is sent to the input of bridge rectifier BR1. The pulsating DC output from BR1 is sent to the voltage regulator's DC input. Power from a DC wall wart should be fed directly to the DC Input pins. DC Wall wart power generally needs more filtering. C1 reduces the ripple in the DC supply. A larger capacitor may be substituted for C1, that is generally only needed for higher power loads. The smoothed DC power is fed to the input of VR1, the 7809 regulator. The 7809 produces 9V regulated DC at the output side. C2 filters load ripple on the output side of VR1. The regulated and filtered 9V DC supply is sent to the load device via 9V battery clips. The 9V DC power is also sent to an optional LED, a high brightness red LED is a good choice here, but almost any LED will work.

Wall Wart Selection

Wall warts can often be found for very small prices at yard sales and second hand stores. However, printed wall wart voltage and current ratings are often very inaccurate and the output voltage can drop a lot under load. It should be possible to sort through a collection of transformers to find ones that are suitable for use with this circuit. Generic wall warts with an output rating of 12VDC are usually a good bet for this application.

Voltage Tests

Before connecting the wall wart to the 9V regulator circuit, check the wall wart's output with a volt meter. The output of DC wall warts should be in the range of 11-16VDC for use with this circuit. The output of AC wall warts should be between 9-14VAC. Connect the DC wall wart supply to the regulator circuit or connect the AC wall wart to the bridge rectifier in front of the regulator circuit.

With the transformer plugged in and nothing connected to the output, measure the DC input voltage to the 7809. It should be a minimum of 11V for proper regulation. If the DC input voltage is raised too high, the 7809 may become very warm. 16V is a good input voltage upper limit. A larger heat sink and bigger container should be used if the circuit is to be used with higher input voltages and/or load currents that approach the 1 amp maximum rating of the 7809 regulator IC. If the output is at a steady 9V, connect the load (pedal) and measure the VR1 input and output voltages, the output voltage should remain at 9V and the input voltage should stay above 11V for good regulation. If the output voltage drops below 9V with the load connected, the wall wart's current rating is probably too low for the load. Substitute a wall wart with a higher current output rating.


The battery eliminator circuit is simple enough to wire with a direct point-to-point construction style. A small piece of perforated board also makes a good base for the project. Just be sure that no wires can cross if the external leads are pulled on. Small bits of black electrical tape can be wrapped around various connections to prevent shorts.

With a little effort, the regulator circuit can be built so that it fits into a 35MM film cannister. A small notch should be cut in the edge of the cannister to allow the wires to pass through. The wires should have a knot on the inside of the cannister to keep them from pulling on the internal components. The small film cannister is best for small loads, larger devices will cause the voltage regulator to get hotter and will need more air space and a bigger heat sink. For setups that approach the 1 Amp current limit of the 7809 regulator, the circuit should be mounted in a small aluminum box and the regulator should be bolted to the side of the box for good heat dissipation.

Be sure to compare the polarity of the adapter's battery snap to a 9V battery, reversed polarity can damage some guitar pedals. Some pedals use a coaxial DC power connector for auxilliary power. If you can find the appropriate mating connector, that is the preferred way to connect the battery eliminator. Be sure to observe the correct polarity on the connector, it varies from device to device.


Plug the battery snap into the pedal's internal battery connector and plug the wall wart transformer into an outlet, connect the guitar and amplifier cables and you're ready to go. It may be possible to use one of these power adapters for more than one effect, this depends on the effect's battery ground polarity as well as the current consumption of the combined pedals. Generally, it is best to use one power adapter per effect pedal, this also lowers the the chance of creating hum from a ground loop.

Other Output Voltages

If the DC device you wish to power uses something other than 9V, this circuit can be adapted. For a 6V DC ouput, replace the 7809 regulator with a 7806 regulator. A 3V DC output can be achieved by using an LM2737ED-3.3 device, those can be purchased at Jameco.com. In general, the input voltage to the voltage regulator should be a few volts higher than the output voltage or the regulator won't be able to do its job. If the input voltage is too high, the regulator may run too hot.

Energy Efficiency

Wall warts are famous for being "phantom loads" that waste power 24-7-365 if they are left plugged in. If you leave a bunch of wall warts plugged in all of the time, your monthly energy bill will go up. A multi-outlet switched plugstrip makes a good master power switch for a guitar amp and some assorted wall warts, and it will save wear and tear on your amp's power switch.


PS1: Wall Wart power transformer, 12-16VDC or 9-14VAC
BR1: 1 Amp bridge rectifier (used with AC transformer only)
C1: 1000uF 25V electrolytic capacitor
C2: 100uF 25V electrolytic capacitor
VR1: 7809 voltage regulator
R1: 680 ohm 1/4W resistor
LED1: high output red type
Aluminum heat sink, TO-220 size
9V battery snap connector or coaxial DC connector
battery snap conectors may be scavenged from an old 9V battery
plastic film cannister or other plastic box
ReadmoreNine Volt Battery Eliminator Circuit

12 Volt 9 Amp Solar Power Center Kit System

The SPC3 kit contains all of the circuitry for a medium-sized solar power system. It includes a solar charge controller for battery charge regulation, a smart on/off power switch with automatic low voltage disconnect operation and a built-in white LED lighting system. Additional lights and other 12V devices can be connected to the load terminals and controlled by the SPC3. The SPC3 can regulate up to 9 amps of incoming solar power and can switch an external load of up to 10 amps. The SPC3 can be used as a stand-alone solar powered lighting system controller for a one room building or RV/camper. The SPC3 can also be used to power other 12V loads such as radios, communication equipment, small TVs, recording equipment, fans, cameras and more. The SPC3 can be installed in both stationary and mobile environments.

The SPC3 should not be used for powering devices with high surge currents such as large motors or high powered car stereos. The SPC3 charge controller section includes: a battery float voltage adjustment, a red/green Charge/Float state indicator LED and battery equalize terminals for occasional overcharging.
A temperature sensor is included so that solar battery charging is temperature compensated. The SPC3 load controller section includes: a momentary action on/off switch for turning the load power and built-in white LEDs on and off, two bright white LEDs for a built-in light source, a low battery indicator LED that warns of impending shutoff and a low voltage disconnect circuit that disconnects the load when the battery discharges below a preset minimum voltage.

Source : http://www.cirkits.com/spc3/index.html

Readmore12 Volt 9 Amp Solar Power Center Kit System
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