Deep-cycle batteries explained

I am confused by your charger article in the November 2004 issue, referring to "deep-cycle" batteries. I am familiar with ordinary old-fashioned lead-acid batteries and sealed lead-acid (SLA) or Gel-Cell batteries, both of which have been around for many years.

I have purchased a new battery for my golf buggy; 12V, 24A.h SLA. Its charger is a simple voltage-sensing device that cuts back to a trickle when the battery has reached a pre-determined voltage. When I asked about "deep-cycle" batteries the salesman looked at me blankly. So exactly what are they? (G. H., via email).

Deep-cycle batteries are made to be discharged down to a certain level before charging. They have a different chemical make-up to standard (car) batteries that are designed for only a shallow discharge. SLA batteries used in golf carts would be a deep-cycle type since they can be discharged below 20% of their capacity before charging.

Signal problem with boost controller

I have just bought some of your new automotive kits from the "Performance Electronics for Cars" book. They are the Fuel Controller and Independent Boost Controller. I would like to use the boost controller to control a diesel injection pump (to control boost pressure to the fuel enrichment diaphragm). The problem is that the boost controller relies on a duty cycle signal.

In a diesel I don’t have that option. Could I fit an analog to digital converter between a boost pressure sensor and boost controller to change the signal? I like the new kits; easy to assemble, with well-written directions. (B. G., Napier, NZ).

Sorry, the input needs to be a duty cycle signal. An analog to digital converter does not do the same job.

A voltage to duty cycle inverter is what you would need. Similar designs for this include pulse width modulation using the TL494.

Large screen scope wanted

Did you ever do any projects on building an oscilloscope or a front-end unit that plugs into a TV for that purpose? (M. M., Mossel Bay, South Africa).

We have not done a project along the lines you describe. A better approach is to use our Sound Card Interface from the August 2002 issue and team it up with oscilloscope software to use with your PC (details in the same issue).

False Triggering Smoke Alarm Control Panel

I have bought two Smoke Alarm Control Panel kits, as described the January & February 1997 issues. The first I assembled in April 1998, using five Kambrook SD29 Smoke Detectors. This has been in continuous use ever since and generally very satisfactory. The regulated supply to the detectors has been checked several times and is always about 8.9V and the battery float voltage always indicates close to fully charged.

We have been very concerned with periodic false alarms with the second unit. These are not due to any smoke, visible or invisible, nor vapours from kitchen or bathroom. The system can operate for months without any action but then typically in the early morning hours, say about 4AM, or it could occur in the middle of the evening or even during the daytime, one detector will emit very brief ‘pips’ or weak ‘beeps’ for a few seconds and then may cease or do the same after a short while, or again it may go on to full alarm output and set off all the others (as it should).

This behaviour seems to occur about October or November. We have guessed that it may be caused by pollen in the air. Do you think this is possible and have you received any other complaints of strange behaviour? (R. B., Flaxton, Qld).

It is possible that one of your smoke detectors is too sensitive. Perhaps your detectors could be checked using a candle or similar to determine if one of them is too sensitive. Alternatively, one of the smoke detectors could be faulty.

MP3 Player startup fix If you’ve built the remote control MP3 player featured in the September & October 2001 issues of SILICON CHIP, you may find that the LCD displays "garbage" characters every time you power up your PC. This is caused by Windows querying the port for a serial mouse as it starts. If you’re a seasoned microcontroller programmer, you can change the "startup delay" parameter stored in EEPROM to stop this from happening. However, a much simpler solution is to send a string of characters to the LCD display to clear it (or display a message) each time Windows starts. We’ve created a simple DOS batch file, called LCDMSG.BAT, that does just that. It contains only two lines; the first initialises the serial port, and the second sends the contents of the text file LCDMSG.TXT to that port. You can edit the file with any text editor (eg, Notepad) to change the COM port number to suit your system. You can also edit LCDMSG.TXT in order to display any custom message that you like. Don’t edit or delete the first few characters though; they’re embedded control codes that are used to clear the LCD display. CLEARLCD.ZIP contains both of the above mentioned files and can be downloaded at the end of this article. Simply unzip it into your C:\Program Files\IRRemote directory and placed a shortcut to C:\Program Files\IRRemote\LCDMSG.BAT in your Startup folder.

Controlling a Peltier tile

I’m looking at operating a Peltier function tile via a parallel port connection to my PC. My intention is to drive the tile and record feedback of temperature variations.

Are there any kits available that will enable me to do this. Any additional advice would be much appreciated. (F. E., via email).

If you only need 8-bit accuracy for the temperature measurements, then the Parallel Port I/O Card published in January 2000 might be suitable (DSE cat K-2805).

You will need to design your own circuit to interface between the card’s open-collector outputs and the power switching circuit for the tile. The same goes for the analog input, where you’ll probably need a buffer circuit for the temperature sensor.

Alternatively, check out the USB I/O 24 card from Elexol (Phone 07 5574 3988). It supports the DS18B20 direct-to-digital temperature sensor, so no additional circuitry will be required on the input side.

2-channel guitar preamp problems

I have built the 2-channel guitar preamp from your November 2000 issue, with varying success. The preamp sounds great but the treble control doesn’t work on either channel. Also I cannot get the digital reverb board to work. All the input voltages are correct and the polarities are correct, according to the testing section of the article. I was hoping for a direction to look in and whether the two problems are related? (A. S., via email).

Treble control and reverb operation are unrelated. Make sure the correct value components are used for this control (ie, the pot and capacitor in series with the potentiometer wiper).

The Reverb unit may have a bad solder connection on the PC board or an incorrect component. Recheck the PC board for shorts between tracks or breaks in the tracks.

Charging SLA batteries in a car

I hope you can help me with information on charging SLA (sealed lead-acid) batteries. I want to charge and use an SLA battery in my car to run accessories when the car is turned off. My car runs at 14V which I believe will charge the battery whilst the car is running. Is there a maximum time I should leave the battery on charge? My understanding is that it would be OK to leave it connected as it would act like a second car battery and as the battery reaches 14V, it will stop excepting charge. Is this true? (S. B., via email).

Charging an SLA battery in parallel with a car battery presents problems. Normally, you should not exceed 13.8V across an SLA whereas car batteries can be charged to over 14V. Connecting an isolating diode is also necessary otherwise the SLA battery will be subject to heavy discharge while you are starting the vehicle. However, an isolating diode will also mean that the SLA battery is unlikely to be charged much above 13.5V (if you’re lucky) so it will never be charged properly. You also need to make sure that the SLA battery is never discharged below about 11V otherwise it will be destroyed.

We suggest you consider building the Adjustable DC-DC Converter for Cars, published in the June 2003 issue. This can be set to charge SLA batteries.

50MHz frequency meter display problem

I have purchased a 50MHz Frequency Meter kit (SILICON CHIP, October 2003) from Dick Smith Electronics (Cat K7001). I need to purchase several ICs as replacement items. These are the MC10116P triple ECL differential line receiver, the 74HC132 quad Schmitt trigger and the PIC16F84-20P programmed microcontroller.

Do you have a contact where I can purchase these items. I would dearly appreciate your assistance with this so I can get my project up and running.

My problem is that the LCD only displays one segment during the initial setup testing procedure instead of "0 Hz". I have triple checked all the components for correct type, location and orientation but still have no joy. Any assistance you could provide me would be terrific. (C. W., via email).

The ICs are unlikely to be faulty. If they are, you can get replacements from the DSE kit department.

Probably the fault is a short between tracks or a broken connection somewhere.

Class-A headphone amplifier wanted

Back in 1998 you designed a 15W class-A amplifier and Altronics still sells it (Cat K5109). I’ve been using one for quite a while now and I have spare amp modules. I was interested to know if these amps could be modified just to run headphones. I have been building amplifiers for a while now. I started with the ETI-5000 and even tried your 100W Ultra-LD amplifier and others but none quite sings like your class-A design.

I found a dedicated headphone class-A amplifier on http://headwize.com/projects/showfile.php?file=gilmore3_prj.htm but the PC board design leaves a lot to be desired and is overly complicated for class-A. Your PC boards are very well laid out. Any suggestions would be greatly appreciated. (A. W., via email).

You could certainly modify the 15W class-A modules to drive headphones although they could drive them unmodified, of course.

If you just wanted to drive headphones, the quiescent current could be dropped to 100mA and you could substitute cheaper output transistors such as TIP2955 and TIP3055, as used in the SC480 modules. With the reduction in output stage power dissipation to around 4W per channel you can use much smaller heatsinks and a transformer with a much lower power rating could be substituted.

Note that we have not done any of these mods.

More detail wanted on kit projects

I’ve been buying SILICON CHIP magazine for about two years now, with the main intention of teaching myself electronics. To this end, I found the Prawnlight project in the January 2005 issue a little light on detail.

For a while I had trouble working out why the transistors were necessary and why just resistors alone would not suffice. I ended up concluding that the three diodes were used specifically for their known 0.7V voltage drop to provide a 2.1V reference voltage for the base of Q17 so that the LEDs don’t gradually dim as the battery is depleted. Is this correct? The purpose of the two capacitors has me totally stumped.

What I found really disappointing was the lack of detail about the LEDs, and the fact that I could not find any data on C8050 transistors in the data section of the Dick Smith Electronics catalog. This effectively rules out anyone using their "junk box" to source parts. (T. L., via email).

As stated in the article on page 67, the circuit uses constant current drivers. This is so that the LEDS don’t dim as the battery discharges.

Q17 provides a voltage reference to the bases of all driver transistors, so that they do operate as constant current sources. You could use any white LEDs; the brighter, the better.

The two capacitors are included as a stability measure. Without them, there is a possibility that Q17, which is configured as an emitter follower, could oscillate supersonically. It is not well known that emitter followers can oscillate but it is quite common if these precautions are not taken.

The C8050 are general purpose NPN transistors. You could substitute almost anything: BC548, BC338, PN100 etc. Just watch the pinouts.

We do try to include a lot of circuit detail in our articles but it is not possible to include all the circuit incidentals in every article. If we did, the magazine would be twice the size.

SMS Controller voltage tolerance I’m trying to build the SMS controller featured in your October & November 2004 issues and I’ve purchased the Jaycar kit (KC-5400) to do so. I’ve completed assembly and have started to follow the checkout procedure in part 1. Along the way I’ve discovered some problems. The +5V checks are all good. I have problems, however, with the phone supply section. Unloaded, the phone supply gives 7.1V (article says 7.0V) but loaded with the 10Ω 5W resister, I get 4.2-4.3V instead of the desired 3.6-3.9V. Is this too much? I have checked out my parts placement and believe it to be correct but I’ve noticed the following: (a) the two 1.5Ω resisters are within 5% (correct) but when wired in parallel and measured, the "on board" resistance is 0.9Ω, not 0 .75Ω. Is this an issue? (b) Jaycar have substituted a 220mH 5A ferrite choke for L1. Part size and placement aside, would this cause changes to voltages? (c) IC5 is supposed to be an MC34063. I assume "MC" is for Motorola? The kit includes a chip with the following designations for IC5: ST - brand? CHN - country of origin [China] ? 063EB - part number? K12129 - batch? Is this replacement suitable? At this point, I’m am at a loss as to what to do next. Any suggestions would be greatly received. (G. W., Auckland, NZ). The answers to your questions are as follows: (a) two 1.5Ω 5% resistors in parallel should measure between 0.712Ω and 0.787Ω. You either have a faulty resistor or your multimeter is not accurate enough to measure these low resistances (many are not). Also note that in-circuit measurements can be misleading. (b) the physically larger Jaycar choke won’t alter the output voltage. (c) the "MC" prefix is for Motorola (now On Semiconductor). "ST" is for ST Microelectronics, whom we assume are a second source for the original part. So yes, it should be OK. The higher voltage is most likely due to tolerances in the peak voltage sensing of the 34063, as well as in the 1.5Ω resistors and even the 10Ω test resistor. It is quite normal for the output voltage to change when the input voltage is varied. This is because the circuit is limiting peak current (not regulating voltage) once the output drops below about 7V. The voltage under load is higher than we would have anticipated (meaning slightly higher charging current to the phone) but it is still within operating parameters. You can safely use it as is. Alternatively, you can reduce the charge current back below 400mA by replacing one of the 1.5Ω resistors with a value of 1.8Ω.

Reluctor ignition misses at idle

I built your High Energy Ignition kit (SILICON CHIP, June 1998) and have had it connected to a points-style system without any problems. I have now upgraded to a reluctor style ignition system which worked fine using the factory igniter until recently when it died. The igniter is $160+ new, so obviously I wanted a cheaper way out of the problem with the same or better performance.

I have now converted the HEI kit to the reluctor circuit, taking out the points components and have checked the circuit many times. The circuit works fine and the car has awesome performance up in the high revs but it misses at idle speed.

The spark plugs, HT leads and distributor cap etc are all new and there is no missing above 1500 RPM but the car hardly idles. Would this have anything to do with the sensitivity of the reluctor circuit as it needs to reach a certain speed before the reluctor outputs enough volts to fire correctly? (D.S., via email).

The sensitivity of the reluctor circuit can be improved by varying the 47kΩ resistor connected to the cathode of ZD5. Substitute a 200kΩ trimpot and adjust it so that the circuit works at idle. Then replace it with a fixed resistor of the same value.

Clifford cricket diode confusion

We recently assembled Clifford the Electronic Cricket (SILICON CHIP, December 1994). It had its moments and we just about got there in the end. Well, almost. The problem is that once the battery is connected, although Clifford does his chirping bit correctly, his eyes stay on all the time. Could this have something to do with the orientation of the diodes? It is rather confusing but everything we have read on the internet (including the diode’s product manual!) states that the cathode end of the diode is the one with the stripe.

The diagram says to place the "A" anode end near the 3.3kΩ resistor but in an earlier post on your website regarding Clifford, you state "The anode (A) is the end of the diode with the stripe. Both anodes for D1 and D2 should be toward the 3.3kΩ resistor" which would mean that ours is theoretically the wrong way around. Which way should it be? We would love to get it working fully. (S. J., via email).

The cathode is the striped end of a diode. On Clifford, the cathodes for both diodes D1 and D2 are oriented toward the 470kΩ resistor. The anodes are toward the 3.3kΩ resistor, as marked on the PC board component overlay diagram.

Non-centre-tapped transformers will work

I recently bought a pair of very well-made 300VA transformers with multi-tapped 64V secondaries, intending to use them in high-quality audio amplifiers (ETI488 modules, which I prefer over all others) which need a ±45V DC supply rail. However, it turns out that there is no AC centre tap on the transformers: the closest is at 31/33V AC on the secondary.

At first, I was inclined to reject the transformers as being unsuitable for my application but on reflection, I realise that they will in fact deliver ±45V DC in a conventional bridge rectifier arrangement but with slightly more ripple and current capability than one would expect with a secondary winding tapped at the centre.

My question is this. If I use large filter capacitors (eg, two 22,000μF 50V low-ESR electrolytics), will there be much degradation in the amplifier’s performance? My suspicion is that there will be a measurable but inaudible degradation, but I would be interested to hear the views of the experts at SILICON CHIP. (B. K., via email).

Our guess is that the transformer will supply around ±46V but the higher voltage section (33VAC) will do most of the work. Also you will have a high component of 50Hz ripple rather than the normal 100Hz. The amplifier will still work although it might have higher hum than if the correct supply was used. Apart from that, we would expect no degradation in performance.

Ceiling fan power consumption

How much does it cost to run a ceiling fan, eg, flat out all day. (G. C, Brisbane, Qld).

It depends on the fan’s power rating and your power tariff. If we assume your fan pulls 200W when going flat out, it will then use 4.8kWh in a 24-hour day. Multiply this by your power tariff of say, 12 cents a kilowatt-hour (you will find the tariff on your power bill) and the answer is 48 cents. That’s a lot less than running an air conditioner.

Active crossover question

I have purchased the Jaycar Active crossover kit which was published in your magazine in January 2003. If I understand correctly, all resistors which are 10kΩ and 20kΩ and all capacitors which are 2.2nF and 47nF need to be changed in order to set crossover frequencies. There appears to be one exception – the 10kΩ resistor on the input. Could you please confirm if this is correct?

I have looked carefully through the article and instructions provided with the kit and can’t find information on exactly which resistors and capacitors need to be changed for different crossover frequencies. Only a few of them are nominated as C, 2C, R, & 2R which need to be changed. It is clear that many others need to be changed as well but it’s not possible to tell which ones based on the information given.

In fact, there are quite a few which I’m not sure should be changed. This is misleading as some may just change the values you have marked! (P. S., via email).

IC1a is an input buffer and its 10kΩ input resistor does not need to change. Depending on which crossover frequencies you want to change, the relevant 10kΩ, 20kΩ, 2.2nF and 47nF values need to change. For example, if you want to change the LP (low pass) frequency, you need to change the relevant resistors and capacitors associated with IC5d & IC5c.

NOTES & ERRATA PICAXE Freezer Thermostat (Circuit Notebook, March 2005): The serial programming input (pin 2) and output (pin 7) for IC1 (page 73) are shown connected in reverse.

WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable.