Voltase hobby: universal

Showing posts with label universal. Show all posts

Sunday, November 9, 2014

Constructing a Universal Power Supply using LM317 Rise

This is a basic, Universal Power Supply voltage regulator circuit using an LM317, 3-terminal regulator in a TO-220package. The Universal Power Supply output voltage can be set to anywhere in the range one.5V to 30V by selecting resistances. By using a potentiometer, R2, as of the resistors you can dial up the output voltage wanted. Either AC or DC input can be supplied to the PCB by a socket or terminal block. Connection can be either way around. This is because they have provided a bridge rectifier on board. The input DC voltage to the regulator must be at least two.5V above the necessary output voltage. An off/on switch is provided.

For lots of applications (say 12V at 60mA) a heat sink wont be required. The LM317 will provide slightly higher output voltages than 30 volts. However, for most hobbyists over 30V wont be needed. So to make a small PCB they have used some electrolytic capacitors rated to 35 volts. To be safe for continuous operation the maximum input DC voltage to the regulator ought to not be over 33V. With a two.5V to three.0V drop across the regulator this will give a regulated output of 30V. You can draw up to one.5A from the LM317. In case you need higher then use an LM338T rated to 5A.

When outside capacitors are used with any IC regulator it is lovely practice to add protection diodes to prevent the capacitors discharging back in to the regulator in the event of abnormal operating conditions, like a sudden short circuit on the input or the output, or a back emf from an inductive load. That is the function of D one and D Two.

The worth of R1 can range anywhere from 120R to 1200R However, circuits from most other sources settle on using either 220R or 250R. They have used 240R or 250R. The voltage drop across R1is one.25V for all values, and this is the key to the design. one.25V is the reference voltage of the regulator. Whatever current flows through R1 also flows through R2, and the sum of the voltage drops across R1 and R2 is the output voltage. (Additional current Id also flows in R2 but it is usually 50uA so is negligible.)

The design formula are:

VOUT = 1.25 (1 + R2/R1) volts, or alternatively

R2/R1 = (VOUT/1.25) - 1

So in case you know VOUT & R1 is 250R then you can calculate R2. In case you find that the 5K potentiometer used forR2 does not give you the degree of fine control over the voltage output range that you need then you can use these formula to fine-tune R1 & R2 to better suited values.

Universal Power Supply Schematic Diagram

Wednesday, September 10, 2014

Universal Ding Dong

One frequently finds gongs or chimes for sale in antique shops or Eastern markets. But supposing one would want to wire these to a pushbutton at the front door to create a ding-dong doorbell? How would this be done? Or consider, for a moment, more creative possibilities. How would one e.g. cause wine-glasses or African drums to resonate when a doorbell is pressed?

The schema shown in Fig. 1 provides a mechanical means of striking two gongs or chimes in sequence -- one when the doorbell is pressed, the other when it is released. This it does by briefly activating two solenoids in succession -- or even two motors to which suitable hammers are attached. It is a schema which was rejected by a publisher, for the reason that it was thought to be too complex -- which really it is. I had been designing various embodiments of the same idea, and this embodiment was not the most elegant. Having said this, it works perfectly well.

The schema is unusual from the point of view that it is based on two pulse shorteners, IC1a and IC1b. These are essentially two monostable timers with special arrangements at their inputs. Of critical importance, in these diagram, is that the potential between S1 and R1 should change fairly rapidly when S1 is pressed, and that the trigger inputs of IC1a and IC1b should be suitably biased.

C2 serves to debounce pushbutton switch S1 – however, its value cannot be too high, due to the requirements of the pulse shortener schema. TR1 and R2 serve as an inverter. IC1a is effectively a negative-edge-triggered monostable timer, so that when pushbutton switch S1 is pressed, IC1as output goes “high”, TR2 conducts, and solenoid SOL1 is activated. D1 suppresses back-EMF, which could potentially destroy the IC.

When pushbutton S1 is released, C2 rapidly discharges through R1. IC1b is effectively a positive-edge-triggered monostable timer, so that when IC1bs output goes "high", TR3 conducts, activating solenoid SOL2. D2 is again provided to suppress back-EMF. R9 and R10 are not strictly necessary in the schema, but limit damage in the unlikely event of the failure of TR2 or TR3.

Unless a large battery is used for B1, C1 is needed to provide the "whack" required for solenoids SOL1 and SOL2. If the pulses which activate SOL1 and SOL2 seem to be too long or too short (they are less than a tenth of a second each as shown), the values of R7 and C5, respectively R8 and C6, may be adjusted according to the formula t = 1.1 R C seconds. TR1 is a miniature MOSFET. If an equivalent is required, it may be replaced with the same MOSFET as is used for TR2 and TR3. If TR2 and TR3 are not to be found, rough equivalents may be used, on condition that their gate voltage is at least a quarter below the supply voltage.

Ideally, solenoids SOL1 and SOL2 would be 12V push-action types, or pull-action types which have a thrust pin at the back. However, plain pull-action types should work if they are touching the chimes or gongs when the schema is at rest (they would then pull back, bounce, and strike). Small DC motors may be used with hammers attached, with suitable series resistors if required. These would likely need longer timing periods for monostable timers IC1a and IC1b.

The schema may use the (original) bipolar version of the 555 timer IC, or its more recent CMOS equivalents. If a CMOS equivalent is used, standby current is likely to be below 2mA. That is, an AA alkaline battery pack would last about two months on standby. For longer periods, a regulated power supply is recommended. The supply voltage will ideally be 12V, but may be reduced to 9V.

Copyright Rev. Thomas Scarborough
[Contact the author of this article at scarboro@iafrica.com]

Friday, September 5, 2014

Low Cost Universal Battery Charger Schematic

Low cost solution for charging of both NiCd and NiMh batteries

Here is the schema diagram of a low cost universal charger for NiCD - NiMH batteries. This schema is Ideal for car use. It has ability to transform a mains adapter in to a charger . This one can be used to charge cellular phone, toys, portables, video batteries, MP3 players, ... and has selectable charge current. An LED is located in schema to indicate charging. Can be built on a general purpose PCB or a veroboard. I hope you really like it.

A Low Cost Universal Charger Circuit Schematic

Circuit diagram:

a_low_cost_universal_charger_schema_diagram_for_nicd

A Low Cost Universal Charger Circuit Diagram

Parts:

R1 = 120R-0...5W
R2 = See Diagram
C1 = 220uF-35V
D1 = 1N4007
D2 = 3mm. LED
Q1 = BD135
J1 = DC Input Socket

Specifications:

Ideal for in car use.
LED charge indication.
Selectable charge current.
Charges Ni Cd or NiMH batteries.
Transforms a mains adapter into a charger.
Charge cellular phone, toys, portables, video batteries …

Features:

LED function indication.
Power supply polarity protected.
Supply current: same as charge current.
Supply voltage: from 6.5VDC to 21VDC (depending on used battery)
Charge current (±20%): 50mA, 100mA, 200mA, 300mA, 400mA. (selectable)

Determining the supply voltage:

This table indicates the minimum and maximum voltages to supply the charger. See supply voltage selection chart below.

Example:

To charge a 6V battery a minimum supply voltage of 12V is needed, the maximum voltage is then 15V.

Voltage selection:

Voltage Selection Chart For Low Cost Universal Battery Charger

Determining the charge current:

Before building the schema, you must determinate how much current will be used to charge the battery or battery pack. It is advisable to charge the battery with a current that is 10 times smaller then the battery capacity, and to charge it for about 15 hours. If you double the charge current , then you can charge the battery in half the time. Charge current selection chart is located in diagram.

Example:

A battery pack of 6V / 1000mAh can be charged with 100mA during 15 hours. If you want to charge faster, then a charge current of 200mA can be used for about 7 hours.

Caution:

The higher charge current, the more critical the charge time must be checked. When faster charging is used, it is advisable to discharge the battery completely before charging. Using a charge current of 1/10 of the capacity will expand the lifetime of the battery. The charge time can easily be doubled without damaging the battery.

Note:

Mount the transistor together with the heatsink on the PCB, bend the leads as necessary. Take care that the metal back of the transistor touches the heatsink. Check that the leads of the transistor do not touch the heatsink.

Thursday, August 28, 2014

Universal Laptop Power Supply AC DC Adapter

One of the things you may not think about when buying a new laptop is what will happen if you lose your laptop AC adapters. Sure this does not seem like something you would lose, but it is very easy to misplace. So it is always a good idea to know where to buy another one, or even have another one handy just in case something like this should ever happen.

If you are going to buy laptop AC adapters online you need to make sure it is the right one. The one that comes with the computer is, of course, the best one to have for it, however, if you buy one online just make sure it is going to fit your computer.

Also, be sure that it is a good model of laptop AC adapters. Some of them can get too hot and overheat. The best thing to do is read some online reviews of the notebook battery chargers, and see which ones work the best. From there you can choose the one that you are going to need. I think it is always a good idea to have a back up anyway. Nothing is worse than having a laptop and not being able to use it. So do not let that happen to you. Go out and get an extra one today.

Replacing notebook power supplies is sometimes an expensive process as it the purchase of an air/auto power supply for your laptop. However for those users who need a new power supply for their notebooks or for users planning to travel, Targus have available a Universal adapter series called the Universal 70 Watt AC/DC Power Adapter that gives the user a variety of ways to power their notebooks.

Features

Power on the go, anywhere: Works at home, office, car, boat, or aeroplane.
Lightweight design: At just 213g, this adaptor is lightweight, compact and ideal for travel.
Compatible with other mobile devices: With the optional Targus Accessory Powering System and device tips, you can power your mobile phone or PDA as well as your notebook.

Basically the Universal 70 Watt AC/DC Power Adapter allows you to plug your laptop into a car cigarette lighter, an aero plane power seat system or into the mains to give your notebook the electricity needed to run the unit. Best of all, the device is 98% compatible with popular 70W notebooks and covers a whopping 6,300 models.Visit Tagus Website

Technical Specifications

Compatibility: Airline Compatibility Chart Always call your airline to confirm inflight power seat system and Targus auto/air compatibility.
Varied models of Acer, Apple, Compaq/HP, Dell, Fujitsu, IBM, Panasonic, Sony and Toshiba.
Other: Includes9 tips 91cm AC input cord 91cm DC input cord 1.82m DC output cord User guide.
Size: 13.7 x 5.5 x 2.2 cm.
Technical: 100-230 VAC 11.75-16.00 VDC.
Warranty: Limited Two Year Warranty.
Weight: 213g

Targus Universal 70 Watt AC/DC Power Adapter is a must have device for those notebook users who travel or even for users that need a second power supply for their PC. The unit is relatively quite small and does not weigh much which is perfect for users on the go.