Monday, October 7, 2013
Rear Fog Lamp For Vintage Cars
According to current legislation in many countries, vintage cars must also be fitted with a fog lamp at the rear. In modern cars, there is a bit of circuitry associated with the fog lamp switch to prevent the fog lamp from going on when the lights are switched on if the driver forgot to switch it off after the last patch of fog cleared up. The circuit described here extends that technology back in time. The circuit is built around a dual JK flip-flop (type 4027). T3 acts as an emitter follower, and it only supplies power to the circuit when the lights are switched on.
For safety reasons, the supply voltage is tapped off from the number plate lamp (L2), because it is on even if you accidentally drive with only the parking lights on. The wire that leads to the number plate lamp usually originates at the fuse box. As the states of the outputs of IC1a and IC1b are arbitrary when power is switched on, the reset inputs are briefly set high by the combination of C1, R1 and T1 when the lights are switched on (ignition switch on). That causes both Q outputs (pins 1 and 15) to go low. IC1a and IC1b are wired in toggle mode (J and K high).
The Set inputs are tied to ground (inactive). The driver uses pushbutton switch S1 to generate a clock pulse that causes the outputs of the flip-flops to toggle. The debouncing circuit formed by C2, R4 and T2 is essential for obtaining a clean clock pulse, and thus for reliable operation of the circuit. C1 and C2 should preferably be tantalum capacitors. The Q output of IC1b directly drives LED D1 (a low-current type, and yellow according to the regulations). The Q output of IC1a energises relay Re1 via T4 and thus applies power to the rear fog lamp L1.
Circuit diagram:
Rear Fog Lamp Circuit Diagram For Vintage Cars
Free-wheeling diode D2 protects T4 against inductive voltage spikes that occur when the relay is de-energised. In older-model cars, the charging voltage of the generator or alternator is governed by a mechanical voltage regulator. These regulators are less reliable than the electronic versions used in modern cars. For that reason, a Zener diode voltage-limiter circuit (D3 and R9) is included to keep the voltage at the emitter of T3 below 15 V and thus prevent the 4027 from being destroyed by an excessively high voltage.
The supply voltage for the circuit is tapped off from the fuse box. An accessory terminal is usually present there. Check to make sure it is fed from the ignition switch. The pushbutton switch must be a momentary-contact type (not a latching type). Ensure that the pushbutton and LED have a good ground connection. Fit the LED close to the button.
The following ‘Bosch codes’ are used in the schematic:
- 15 = +12 V from ignition switch
- 58K = number plate lamp
- 86 = relay coil power (+) IN
- 85 = relay coil power OUT
- 30 = relay contact (+) IN
- 87 = relay contact OUT
Author: Eric Vanderseypen - Copyright: Elektor Electronics Magazine
Friday, October 4, 2013
A Discharger for Receiver Battery Packs
You may have read about cycling NiCad batteries. If not, read a little here ( Reds R/C Battery Clinic) for an excellent overview. Overcharging apparently leads to voltage depression, which can be corrected by one or two complete discharges (to 1 to 1.1 volts per cell). On the other hand, over discharging the batteries to a low or zero voltage can damage them, and if the batteries have not been overcharged and have no voltage depression, cycling just uses up regular battery life. I designed and use this discharger occasionally to remove voltage depression and insure battery capacity is still ok for those planes that have no low voltage alarm.
Note that the 100 ohm resistors are 1/2 watt (these are the load resistors), the rest are 1/4 watt. The red LED lights while discharging, buzzer sounds and discharge rate drops to 15-25mA (for the buzzer) when complete. The discharge load is 60mA to 110mA depending on the battery voltage. Since thats about the same current draw as my Hitec receiver and two HS-80s draw while flying handlaunch, I can use discharge time almost directly to indicate flying time. The buzzer uses enough current to keep a 150mA battery down, but when discharging a 600mA battery, the battery recovers quickly when the load is removed--the buzzer/discharger cycles on and off. Threshold voltage of the discharger is set to 4.2 volts. Since the discharger still draws some current when buzzing, try to disconnect the discharger once the alarm sounds--dont leave it going for hours lest the battery be over discharged.
There are a couple ways you could modify the circuit to work with a 5-cell 6-volt receiver battery pack. The two 1k resistors are a divider network, so one way would be to change the resistors to change the sampling voltage at the comparator. The formula for a divider network is Vout=Vin(R2/(R1+R2)) or R1=R2*((Vin/Vout)-1). Here, R1 is the resistor connected to the positive lead and pin 7 of the comparator, Vin is 5.25 volts (1.05 volts per cell discharge shutoff threshold), and Vout is the reference 2.1 volts (the voltage produced by the LM317T and the 180 and 270 ohm resistors). You can use R2 as the same 1k value that was there before. So R1=1000*((5.25/2.1)-1)=1500=1.5k. So swap the top 1k resistor in the schematic for a 1.5k, and the new shutoff voltage for your device will be 5.25 volts.
To increase the discharge rate, decrease the resistance of the load resistors. You could use four 100 ohm resistors in parallel instead of two, for example, and it would discharge twice as fast. Resistance of a number of resistors in parallel is the value of the resistor devided by the number of the resistors. Here, 100 ohms/ four resistors is 25 ohms. At five volts, current is (5 volts)/(25 ohms)=0.2 ampere or 200mA. Be careful not to decrease resistance too much however--the small signal transistor used in this particular circuit is probably only rated for maximum 500 mA.
Circuit diagram :
Parts:
273-074 Miniature Piezo Buzzer, 12v, PC board mount
271-312 1/4 watt 5% carbon film resistors, 500 pieces (Just do it!)
276-1778 LM317T adjustable voltage regulator
276-1712 Quad comparator LM339
276-1622 LED assortment (20 count)
276-2009 NPN Silicon transistor MPS2222A (2N2222)
Custom electronics:
I post this design not because I think this is a brilliant piece of circuit design but because the design works, and it can give you a start on your own experimentation. The idea is to use the power available from the discharging battery to monitor the voltage of the battery, shut off discharging at a preset voltage (here 1.05 volts/cell), and sound an alarm when discharging is complete. To do so means a voltage reference powered by the changing voltage of the battery, here the LM317T and the 180 with 270 ohm resistors. You could just as easily use a LM336 (see the low voltage warning buzzer page) or a zener with resistor, or something else as a reference. Since the reference voltage must be below the ambient battery voltage, a pair of 1k resistors provides the divided test voltage. The LM339 is a four way comparator.
This design uses really three comparators: in addition to the one driving the transistor, a comparator drives the LED and another drives the buzzer. But you could use a single comparator (like the LM311) with the buzzer across the emitter and collector of the transistor, and the LED in series with a 270 ohm resistor across (parallel with) the 100 ohm load resistors. With the transistor conducting, the voltage drop across base and emitter is low, and the buzzer is quiet. The tiny current in a piezo buzzer (7 mA), when the transistor is not conducting, would be divided between the load resistors and the LED, and the LED is dark.
A word about the comparator. The output of the comparator serves as a meager source of current, but can sink current nicely. In other words, the high logic output of the comparator will not drive the base of a NPN transistor as here. The 560 ohm resistor provides the current here for the transistor base--the comparator takes it away when its output drops to ground. Hmmm . . . . so, maybe use a PNP transistor like a 2N3906 instead with emitter to + and collector to load, remove the 560 resistor and connect the base through a 1k resistor to the output of the comparator, then reverse the logic of the comparator by swapping the reference with the test. . . hmmmmm. Could work. Yep . . . works.
Source : electronic
Monday, September 30, 2013
Preamplifier For Soundcard Circuit
Friday, September 27, 2013
Low Voltage Cutout For 12V SLA Batteries
However, when the op amp’s output is driven low, Q1 is switched off, causing the non-inverting input to rise towards the full battery voltage. This greatly reinforces the switching action, latching the circuit in the "off" state until the battery is recharged and the reset switch (S1) pressed. The Mosfet used for Q2 should be selected to suit the intended application. The circuit could also drive a relay simply by connecting the coil across the "load" terminals. As is usual practice, a diode should be connected across the relay coil to limit back-EMF spikes.
Monday, September 9, 2013
Now Oyster Releases the First True Netflix for E books App
Oyster, a New York-based startup, made headlines late last year when it broadcast lifting $3 million from Founders finance to construct out a service that would offer "unlimited access" to e-books. On Thursday, the startup commenced its e-reading app for iPhone, which is accessible on a first-come, first-served invitation-only cornerstone for now.
With the iPhone app, users get access to more than 100,000 ebooks from hundreds of publishers including Houghton Mifflin Harcourt, Melville House and one of the "big five" announcing houses, HarperCollins. Oyster will ascribe users $9.95 a month to read as numerous e-books as they like.
"People love accessing things when they desire it with one price," Eric Stromberg, co-founder of Oyster, said in an interview with Mashable. although, he believes a couple of obstacles have held back most startups from endeavouring to do the lone cost subscription form with e-books: "Any company that does this desires to be actually good at technology, at merchandise and on the joint venture side of things, and construction a centre area of know-how in each of those."
Another new ebook startup, is also trying to make the digital publication subscription notion work, but with a very distinct charge form. Rather than charge on flat monthly rate for unlimited reads, eReatah offers three tiered charges extending from $16.99 a month for two reads to $33.50 for four reads a month.
While the tiered pricing form could verify to be a better deal for publishers and authors, Stromberg states his group endeavoured to discover from living digital subscription services and put simultaneously a income model that "really places the rightsholders interest first and makes sense over decades." That said, the group is somewhat open to other charge structures in the future. "If we can provide a large experience kind of in a freemium form, well work in the direction of that," said Willem Van Lancker, one of the three co-founders.
The novelty of the subscription model for ebooks almost overshadows some of the more subtle but important changes Oyster is trying to make to the e-reading know-how. Like Netflix and Spotify, Oyster doesnt just provide easier get access to to content, but furthermore aspires to help users discover and share content. The publications are coordinated into genres similar to Netflix and every client has a social profile in the app and can pursue the reading undertaking of other users theyre connected to. There are furthermore constructed in choices to share books to Facebook, Twitter and even Instagram.
after that, Oyster made the interesting alternative to focus on the smartphone reading experience first, rather than tablets, where one might assume most persons do their long reading. The reasoning, according to the founders, is easy: many more people carry round smartphones than tablets. To make it work, though, Oysters group rethought the e-reading design: Users scroll through the text from peak to bottom rather than right to left, and they have more customizability over font kind and dimensions.
The two large-scale matters for Oyster are of course cost and selection. Oysters 100,000 books encompasses a pleasant variety of classics and up to date titles, but at launch its lacking numerous bestsellers and brand new releases. For the casual client, giving $120 a year for a service like this makes the most sense if you dont have to pay much more on top to read other issues not available to rent. In my own know-how, many of the publications I sought for — from well-known authors like Jonathan Lethem, George Saunders and Anthony Swofford — were unavailable. That may change if the service gets more traction amidst users and thus expanded leverage amidst publishers.
At $9.95 a month, Oyster is slightly more costly than Netflixs streaming-only option. That is a better worth proposition in the sense that you need only lease one ebook a month to at smallest shatter even, while you would need to watch multiple movies or display seasons a month on Netflix to come out ahead of usual rental charges in bricks-and-mortar video stores. Unfortunately, a Pew survey from last year discovered that just 27% of Americans read the matching of one or more publications per month — digital or physical — which proposes the $120/year could be seen as steep cost to pay for many.
For better or worse, the success or malfunction of Oyster may assist as the ultimate litmus check for whether digital apparatus boost the consumption of publications — in the way that they might with movies — or undermine it.
"You glimpse all the times someone says Im really enjoying shattering awful, its on Netflix, you have no apologise not to go at smallest give it a shot. We seem that same way with books," Stromberg says. With an get get access to to form, he states, "You spend less time conceiving about making a buy, less time conceiving about if you should read this publication and actually just start reading it. Thats ultimately the way youll be adept to notify you like it."
Wednesday, April 10, 2013
Deluxe Charge Rate Limiter for Small Capacity NiCad Batteries
Wednesday, April 3, 2013
Dual Power Supply For Amplifiers
They do have some problems, such as higher inrush current at switch on, which means that slow blow fuses must be used. For the 60W amplifier, a nominal (full load) supply of +/- 35V is required, so a 25-0-25 secondary is ideal - however, see Updates, below. The circuit for the supply is shown below, and uses separate rectifiers, capacitors and fuses for each channel. Only the transformer is shared, so channel interactions are minimised. A single ±35V supply (i.e. using only a single bridge and set of filter capacitors) will work just as well in the majority of cases.
The 5A slow-blow fuse shown is suitable for a 300VA transformer, if a 120VA transformer is used, this should be reduced to 2.5A (or 3A if 2.5A proves too hard to get). If you are even a little bit concerned about the fuse rating, contact the transformer manufacturer for the recommended value for the transformer you will use. The correct fuse is critical to ensure safety from electrical failure, which could result in the equipment becoming unsafe or causing a fire.The capacitance used is not critical, but is somewhat dependent upon ones budget. I suggest 10,000uF capacitors, but they are rather expensive so at a pinch 4,700uF caps should be fine - especially in the arrangement shown. When unloaded (or with only light load), the voltage will normally be somewhat higher than 35 Volts. This is Ok, and should not cause distress to any amp. The voltage will fall as more current is drawn, and may drop below 35V if a small transformer (or one with unusually poor regulation) is used.
Two parts of this circuit are critical:
- Mains wiring must be cabled using approved 240V rated insulated cable, and all terminations must be insulated to prevent accidental contact. The mains earth must be securely fastened to the chassis, after scraping away any paint or other coating which might prevent reliable contact.
- The centre-tap of the transformer and the ground points of each capacitor must be connected to the main signal earth point via heavy duty copper wire, or (preferably) a copper bus-bar. Large currents flow in this part of the circuit, containing nasty current waveforms which are quite happy to invade your amplifier. The supply voltages must be taken from the capacitors (not the bridge rectifiers) to prevent unwanted hum and noise.
Bridge rectifiers should be the big bolt-down 35A types (or something similar) to ensure lowest possible losses (these will not require an additional heatsink - the chassis will normally be quite sufficient). The transformer primary voltage will obviously be determined by the supply voltage in your area (i.e. 120, 220 or 240) and be suited to the local supply frequency. Note that all 50Hz transformers will work just fine at 60Hz, but some 60Hz devices will overheat if used at 50Hz.
The transformer should be rated at a minimum of 120VA (Volt-Amps) for home use, but a 300VA transformer is recommended due to its superior regulation. Going beyond 300VA will serve no useful purpose, other than to dim the lights as it is turned on. Where it is possible, the signal and power ground should be the same (this prevents the possibility of an electric shock hazard should the transformer develop a short circuit between primary and secondary. Where this will give rise to ground loops and hum in other equipment, use the method shown.
The resistor R1 (a 5W wirewound resistor is suggested) isolates the low-voltage high-current ground loop circuit, and the diodes D1 & D2 provide a protective circuit in the event of a major problem. These diodes need only be low voltage, but a current rating of 5A or greater is required. The 100nF capacitor (C1) acts as a short circuit to radio frequency signals, effectively grounding them. This should be a device with very good high frequency response, and a monolithic ceramic is recommended.
Updates:
The transformer secondary voltage will probably need to be higher than described above. I tested some stock and custom transformers I have, and found that unless the transformer has extraordinarly good regulation, a nominal 28-0-28 secondary will be needed, more with an average (i.e. poor) regulation unit. Also be careful when you test, since a relatively small (10%) variation in the mains voltage makes a big difference to measured output power - the secondary voltage also falls by 10%, so 60W becomes 48W if the mains is 10% low.
You also need to remember that the output voltage of transformers is typically quoted at full power with a resistive load. This means two things:
- The no load voltage will be higher than expected
- The loaded voltage will be lower than expected
Sunday, March 24, 2013
Rear Light After Glow For Bicycles
Tuesday, March 19, 2013
Electrical Isolation For I2C Bus
Resistors R1, R4, R5, and R8, are the usual 3.3 kΩ pull-up resistors that are obligatory in each I2C line. If these resistors are already present elsewhere in the system, they may be omitted here. The current drawn by the circuit is slightly larger than usual since the pull-up resistors are shunted by the LEDs in the optoisolators and their series resistors. Nevertheless, it remains within the norms laid down in the I2C specification.