Showing posts with label a. Show all posts
Showing posts with label a. Show all posts
Sunday, May 5, 2013
JAM Just A Minute Circuit
This jam circuit can be used in quiz contests wherein any par- ticipant who presses his button (switch) before the other contestants, gets the first chance to answer a question.
The circuit given here permits up to eight contestants with each one allotted a distinct number (1 to 8). The display will show the number of the contestant pressing his button before the others. Simultaneously, a buzzer will also sound. Both, the display as well as the buzzer have to be reset manually using a common reset switch. Initially, when reset switch S9 is momentarily pressed and released, all outputs of 74LS373 (IC1) transparent latch go ‘high’ since all the input data lines are returned to Vcc via resistors R1 through R8. All eight outputs of IC1 are connected to inputs of priority encoder 74LS147 (IC2) as well as 8-input NAND gate 74LS30 (IC3). The output of IC3 thus becomes logic 0 which, after inversion by NAND gate N2, is applied to latch-enable pin 11 of IC1. With all input pins of IC2 being logic 1, its BCD output is 0000, which is applied to 7-segment decoder/driver 74LS47 (IC6) after inversion by hex inverter gates inside 74LS04 (IC5). Thus, on reset the display shows 0. When any one of the push-to-on switches—S1 through S8—is pressed, the corresponding output line of IC1 is latched at logic 0 level and the display indicates the number associated with the specific switch. At the same time, output pin 8 of IC3 becomes high, which causes outputs of both gates N1 and N2 to go to logic 0 state. Logic 0 output of gate N2 inhibits IC1, and thus pressing of any other switch S1 through S8 has no effect. Thus, the contestant who presses his switch first, jams the display to show only his number. In the unlikely event of simultaneous pressing (within few nano-seconds difference) of more than one switch, the higher priority number (switch no.) will be displayed. Simultaneously, the logic 0 output of gate N1 drives the buzzer via pnp transistor BC158 (T1). The buzzer as well the display can be reset (to show 0) by momentary pressing of reset switch S9 so that next round may start. Lab Note: The original circuit sent by the author has been modified as it did not jam the display, and a higher number switch (higher priority), even when pressed later, was able to change the displayed number.
Read More..
The circuit given here permits up to eight contestants with each one allotted a distinct number (1 to 8). The display will show the number of the contestant pressing his button before the others. Simultaneously, a buzzer will also sound. Both, the display as well as the buzzer have to be reset manually using a common reset switch. Initially, when reset switch S9 is momentarily pressed and released, all outputs of 74LS373 (IC1) transparent latch go ‘high’ since all the input data lines are returned to Vcc via resistors R1 through R8. All eight outputs of IC1 are connected to inputs of priority encoder 74LS147 (IC2) as well as 8-input NAND gate 74LS30 (IC3). The output of IC3 thus becomes logic 0 which, after inversion by NAND gate N2, is applied to latch-enable pin 11 of IC1. With all input pins of IC2 being logic 1, its BCD output is 0000, which is applied to 7-segment decoder/driver 74LS47 (IC6) after inversion by hex inverter gates inside 74LS04 (IC5). Thus, on reset the display shows 0. When any one of the push-to-on switches—S1 through S8—is pressed, the corresponding output line of IC1 is latched at logic 0 level and the display indicates the number associated with the specific switch. At the same time, output pin 8 of IC3 becomes high, which causes outputs of both gates N1 and N2 to go to logic 0 state. Logic 0 output of gate N2 inhibits IC1, and thus pressing of any other switch S1 through S8 has no effect. Thus, the contestant who presses his switch first, jams the display to show only his number. In the unlikely event of simultaneous pressing (within few nano-seconds difference) of more than one switch, the higher priority number (switch no.) will be displayed. Simultaneously, the logic 0 output of gate N1 drives the buzzer via pnp transistor BC158 (T1). The buzzer as well the display can be reset (to show 0) by momentary pressing of reset switch S9 so that next round may start. Lab Note: The original circuit sent by the author has been modified as it did not jam the display, and a higher number switch (higher priority), even when pressed later, was able to change the displayed number.
Friday, April 26, 2013
A Handy Pen Torch
This straightforward to construct “Handy pen torch” digital circuit and low part rely, makes use of two power white LEDs for lighting fixtures. Low volt (4.8V dc) supply on hand from the built in rechargeable Ni-Cd battery pack is first converted into two channel (independent) constant current supplys with the support of two items of the in demand precision adjustable shunt regulator chip LM334 (IC1 and IC2). Around 25mA at three.6 volt dc is to be had on the output of these ICs.
This regulated dc provide is used to power two power white LEDs D4 and D6. Resistors R3 and R5 restricts the output present (and hence the light output) of IC1 and IC2 circuits respectively. Besides these parts, one purple colour LED (D2) is integrated in the primary circuit which works as a battery charging provide input indicator. Resistor R1 restricts the operating current of this LED.
This regulated dc provide is used to power two power white LEDs D4 and D6. Resistors R3 and R5 restricts the output present (and hence the light output) of IC1 and IC2 circuits respectively. Besides these parts, one purple colour LED (D2) is integrated in the primary circuit which works as a battery charging provide input indicator. Resistor R1 restricts the operating current of this LED.
Pen Torch Electronic Circuit Schematic
Diode D1 works as an input polarity defend cum reverse current glide preventer. Capacitor C1 is an easy buffer for circuit stabilization. After succesful development, ideally on a small piece of basic purpose PCB, enclose the whole circuit in an acceptable and engaging pen torch cabinet. If important, drill appropriate holes in the cupboard to attatch the dc socket, on/off swap and the enter indicator and many others. In prototype,commonly available 4.8 volt/500mah Ni-Cd battery pack (for cordless phones) is used.
One very simple but dependable ac primarys powered battery charger circuit for the at hand pen torch can also be included here. Basically the pen torch circuit is a continuing current charger wired round Transistor T1 (BC636), energyed by using a 12v/350mA step down transformer and associated elementsD1, D2 and C1.
One very simple but dependable ac primarys powered battery charger circuit for the at hand pen torch can also be included here. Basically the pen torch circuit is a continuing current charger wired round Transistor T1 (BC636), energyed by using a 12v/350mA step down transformer and associated elementsD1, D2 and C1.
AC majors powered battery charger for the pen torch
Unregulated 12 volt dc available from the enter energy convereter circuit, comprising step down transformer(TRF), rectifier diodes (D1,D2) and filter capacitor (C1), is fed to T1 via a current restricting resistor R1. Grounded base PNP transistor T1 here works as a relentless present generator. With 22 ohm resistor for R1, the charging present to be had on the output of the charger is close to 50mA.
Red LED (D3) provides a set voltage reference to the base of T1, with the assist of resistor R2. (During charging course of, Diode D1 in the primary circuit stop reverse current waft from the battery pack when charging input supply is absent.) After construction of the pen torch circuit, match the assembled unit inside of a small plastic enclosure for security and comfort.
Red LED (D3) provides a set voltage reference to the base of T1, with the assist of resistor R2. (During charging course of, Diode D1 in the primary circuit stop reverse current waft from the battery pack when charging input supply is absent.) After construction of the pen torch circuit, match the assembled unit inside of a small plastic enclosure for security and comfort.
Circuit Source: DIY Electronics Projects
Thursday, April 4, 2013
A 12V Car Charger For ASUS Eee Notebook
The ASUS Eee is a fantastic ultra-portable notebook with almost everything required for geeks (and nothing that isn’t). Plus it features fantastic build quality and is very well priced. If you live in New Zealand you can get them from DSE; at the time of writing they are the exclusive supplier. I worked out it’s the same cost as importing one once you include all the duties and tax, plus you get the advantage of a proper NZ-style mains charger. Anyway, being so small I thought it would be nice to be able to carry this around in the car. Unfortunately I couldn’t find a car charger available anywhere at the time so I decided to tackle the problem myself. As a bonus this provides an opportunity for an external high-capacity battery.
Commercial Equivalent:
I thought at this stage it would be worth noting that a commercial car charger is now available for less than it cost me to build this from Expansys and is available in most countries (select your location on their site). It outputs 9.5v from 10-18v in at up to 2.5A. I’d actually recommend it over the design here is it seems to perform better at lower voltages (that one works down to 10V). However I have kept this page up as a reference for those who enjoy tinkering.
Design:
The charger included with the Eee is rated at 9.5v, 2.315A. There isn’t a fixed voltage regulator available for this exact voltage, so the circuit needed to be designed around an adjustable regulator. I decided to design the charger around the LM2576 “Simple Switcher” IC from National Semiconductor. There are tons of ICs like this available, many of which are a bit more efficient, however I selected this one because it is readily available and relatively cheap. It also has a lower drop-out voltage (~2V) than many other chips I looked at which is important when powering the device from a car or 12v SLA battery.
This circuit could have used a standard three pin regulator IC such as the LM317, however most types require an external transistor when handling so much current and not to mention the fact that they are very inefficient; they draw the same amount of current from the input as the load and the difference in power is dissipated as heat. The main problem with using the LM2576 is the fact it needs quite a large inductor due to its somewhat low switching frequency. The inductor I used is made by Pulse Engineering, part number PE92108KNL. I’d prefer a smaller one, however I couldn’t find one capable of supplying the required current that I could purchase in single units. Besides the PE92108KNL is apparently designed specifically to work with the LM257x series.
The circuit also includes a low voltage cut-out based on a 9.1v Zener diode and BC337 transistor that will shut down the regulator if the input voltage is below 11.5V. This prevents unstable operation of the regulator at lower input voltages, and also helps prevent accidental flattening of the supply battery. Substituting this transistor for similar type may affect the cut-out voltage; the Vbe of the transistor should be 1.2v.All of the components used should be pretty readily available in most areas. I got everything from Farnell. Jaycar also sells everything except the inductor. Make sure you specify high temperature, low ESR capacitors as these help result in more stable operation and better efficiency of the charger.
Unfortunately the end result is a charger that is slightly bulkier than I would really like. I attempted to fit this inside an old mobile phone charger case so the whole thing could hang out of the cigarette lighter, however I ran into trouble making the circuit stable enough and dissipating all the heat. Due to the high current involved compared to a mobile phone charger the components are much bulkier so it’s pretty tricky to get all to fit! If I do get it finished I’ll add an update.
Parts List:- 2x 10k resistor (R1 & R4)
- 2x 22k resistor (R2 & R3)
- 1x 1.5k resistor (R5)
- 1x 120μF 25v electrolytic capacitor (C1)
- 1x 2200μF 16v electrolytic capacitor (C2)
- 1x 1N5822 Schottky diode (or equivalent)
- 1x 9.1v 0.5W Zener diode
- 1x BC337 NPN transistor
- 1x LM2576T-ADJ IC
- 1x 100uH, 3A inductor (e.g. Pulse PE92108KNL)
- 25°C/W or better minature heatsink (e.g. Thermalloy 6073)
- Cigarette lighter plug with 3A fuse and 2.1mm DC plug (e.g. DSE P1692)
- 2.1mm DC chassis mount socket
- 1.7mm x 4.75mm (ID x OD) DC plug and cable
- Small plastic enclosure
Make yourself a PCB using the template below (600dpi). I simply laser print (or photocopy) the design onto OHP transparency sheet and then transfer the toner onto a blank PCB using a standard clothes iron. Any missing spots can be touched up with a permanent marker before etching. This is quick, usually results in pretty tidy boards and hardly costs a thing. There is a tutorial on a variation of this method at http://max8888.orcon.net.nz/pcbs.htm.
Install the components on the PCB and triple check the layout before soldering. It is much easier to start with the low profile components such as resistors and diodes, then install the larger components after-wards. Don’t forget the wire link; this is shows as a red line on the layout guide above. Remember to smear a small amount of heatsink compound on the regulator tab before mounting the heatsink.
For a case I used a small plastic enclosure from DSE, part H2840, as it was all the local store had in stock that was remotely suitable. The PCB is designed to fit into this particular case, however any small box should be suitable. If you have a dead laptop charger lying about it might be worth ripping the guts out of that and salvaging the case. If your enclosure is different you may need to modify the design to suit, so I have provided the schematic and PCB design files for download. They were created using Eagle. The Eee uses a standard 1.7mm DC power connector with a positive tip.
Connect the circuit to a 12v supply. If you use a car or lead acid battery ensure you have a 3A fuse fitted in line with the circuit before connecting it, just in case. Use your multimeter to check that the circuit outputs about 9.45v with no load. Connect a 12V, 21W lamp (e.g. old brake lamp from a car) or similar load across the output and check that the voltage doesn’t vary much. You should now be able to connect your Eee. The circuit design should be good for up to 2.5A, so there is plenty of margin for the Eee to fully function and charge its own battery off this supply.
SLA Battery Carry-bag:
Jaycar have a really cool carry bag with a shoulder strap designed to perfectly fit a 12v 7AH sealed lead acid battery. The bag features a fused cigarette lighter socket and is the perfect compliment to this charger. It works well with the Eee and provides hours of extra use. The shoulder strap means it’s not too bothersome to carry about and the charger circuit itself zips up neatly inside the bag. The under-voltage cut-off means the battery will never run completely flat, and the Eee will simply cut over to its internal battery once the SLA runs out. I got my SLA battery from Rexel as they are much cheaper (approx NZ$18 including GST last time I bought one) and they don’t sit as long on the shelf as many other suppliers.
Disclaimer:
This circuit is intended for people who have had experience in constructing electronic projects before. The circuit design and build process are provided simply as a reference for other people to use and I take no responsibility for how they are used. If you proceed with building and/or using this design you do so entirely at your own risk. You are free to use the content on this page as you wish, however I do ask that you include a link or reference back to this page if you distribute or publish any of the content to others.
Source: Marlborough Wi-Fi
Subscribe to:
Posts (Atom)