Speed Controller For Xbox Fans
I have put together the 12-24V Motor Speed Controller (SILICON CHIP, June 1997) for the purpose of controlling the 12V thermo fans for my Xbox 360. At 12V, they are quite noisy so I just wanted to be able to adjust the speed of the fans accordingly. I have two problems.
(1) There is a high-pitched squeal coming from the motors. I have fitted the diode and capacitor before the fans and have tried 1mF, 0.22mF and 0.33mF capacitors as well but they didn’t help. What can I do to remove this noise as it defeats the purpose of the kit?
(2) I installed a larger pot to make it easier to adjust and so I could mount it where I needed it but when you turn it, the fans are at full power and I have only used maybe one third of the dial. Is there a way to make use of the whole dial, thereby making it easier to adjust? (J. B., via email).
You may be able to reduce the noise by changing the frequency. You can vary the 10kW resistor at pin 6 of IC1 from 2kW to 500kW to get a change in frequency from 30Hz to about 10kHz. Use a 500kW trimpot (wiper connected to one end) with a series 2.2kW resistor to replace the 10kW resistor. Adjust this trimpot for minimum noise.
The control pot can be made to work over a wider range by adding a 4.7kW resistor in series at each end of the pot. So one end of the pot connects to ground (0V) via a 4.7kW resistor and the opposite end goes to +5V via a second 4.7kW resistor.
Is your recently published Universal Speaker Protection & Muting Module (SILICON CHIP, July 2007) capable of providing current for two relays? Perhaps Q4 would only need the addition of a heatsink or would other modifications be necessary? I could imagine that someone with a multi-channel amplifier for home theatre or bi-amping would find it useful to run two relays.
In my case, I wish to use your module to remove turn-on thump in a headphone amplifier that is often connected directly to my CD player. The player is also used for the family stereo and rather than change leads when I want to use the headphones I wish to use a second relay with normally-closed contacts acting to bypass the headphone amplifier when power is off and to disconnect the bypass when power is on.
Perhaps if you could provide a figure for the current handling of the circuit, I could substitute a pair of lower power relays as one solution. (K. W., Newport, Vic).
I am intending to build a 5-inch gauge diesel shunter driven with a 12V 18A DC motor and want to use a speed control and drive it forwards and backwards. Do you have a kit that I can use? (B. K., via email).
Amplifiers And Hum Problems
I have two amplifiers which my Dad made and which look like Studio 200 versions judging by the MJ15003 and MJ15004 output transistors. He also had some old SILICON CHIP pages from 1987 & 1988 which describe the Studio 200 (February 1988) and what looks like the full article from the earlier version with other output transistors.
The latter text mentions using different Polyswitches for 4-ohm or 8-ohm loads. I was thinking of adding wires to the PC board terminals and up to a switch and then through either of the Polyswitches and back down to the board. The reason is that I am not sure what impedance speakers I might end up with. Can you see any problem with that or is there a more involved way to achieve the same objective?
Also, I would appreciate any tips you might have for reducing hum from my guitar amplifier. Any lead I plug into the input results in a lot of hum, increasing with the volume adjustment.
It is a brand new Roland guitar amplifier and it is not to do with the guitars that are plugged in. They are a Taylor Acoustic with Fishman pickup and a Les Paul with hum-bucker pickups. There are no single-coil "strat" guitars and not a fluoro for miles. I even turned off every circuit breaker except the one supplying the power point and unplugged every appliance on that circuit too.
The symptoms are: with nothing plugged in and volume up full, there is no hum; with lead and guitar plugged in, heaps of hum; with lead only, heaps of hum and with just an empty jack plug plugged in, heaps of hum. Touching the earth of the jack plug cancels the hum almost totally.
As is the way, I took it back to the shop and it didn’t do it in the shop. The shop guy said it must be relevant to my venue. I tried running an earth wire from the power point through a 50kW pot and on to the earth of the jack plug going to the input of the amplifier but no luck. I also tied one of those clip-on "dongle like things" to no avail.
Across the road is a large shopping centre, with the usual electrical gear and mobile phone towers on top. The electric train line is about 700 metres away. Because there is no noise with nothing plugged in, I’m guessing it’s RF noise, although the input jack might have a shorting arrangement internally. (L. K., via email).
As far as your hum problem is concerned, there appears to be something funny about the earth connection on your jack plug or the sockets themselves. Evidently, the earth side is not making good contact.
I have a question regarding the connection of a ceiling fan. My electrician told me that it was not possible to connect the light for the ceiling fan into a 3-way switch.
Essentially the fan has a remote control that allows you to turn the light on and off. I want to be able to use a wall-mounted switch as well to turn the light on and off. I understand that the output from the remote control unit doesn’t have the ability to connect to the 3-way switch, as it is essentially a 2-way switch but would it be possible to do this using a relay? (A. F., via email).
It may be easier to dispense with the remote control and just have a wall-mounted switch for the lamp or use two-hand held remotes, with one placed on the wall where the 2-way switch is required.
Variable Frequency Supply For Induction Motors
I have a number of of fractional horsepower induction motors collected from old home appliances and picked up at auction sales. However, they would be a lot more useful if I could vary their speed.
I know I can use universal (series) motors with an SCR speed control circuit but it is very hard to run something at a quiet constant speed under a varying load. My problem at the moment is a low-cost scroll saw with a 200W motor running at a constant speed. It would be much more versatile if I could run it fast or slow.
Would it be possible to build a 200W inverter with a variable frequency instead of a fixed 50Hz output? It wouldn’t need to be pure sinewave either. And rather than use a hefty transformer or a switchmode power supply to go from 12V or 24V DC up to 240VAC, could one not rectify the 240VAC mains AC to DC and then chop it back to AC that could be varied from say 20-100Hz? (K. C., Invercargill, NZ).
Some ideas could be obtained from our 2kW Sinewave Inverter (October 1992 to February 1993) and the 200W Modified Square Wave Inverter from February 1994.
I am from the University of Western Australia Motorsport Team (UWAM) and I have a couple of questions you might be able to answer.
We are building an open-wheeled racer and are trying to put all of the circuits on as few boards as possible. Is there a problem with putting high-amp circuits near microprocessors and is there a way of avoiding said problem? Also, what are some good noise reduction techniques that we could employ to ensure the best quality signal, especially given that everything is constantly moving throughout the race? (Z. B., via email).
However, it does require careful layout of the PC board to ensure that the high currents do not flow in the signal sections of the microcontroller and that the high currents do not induce unwanted signal voltages into sensitive parts of the circuit.
I have built the Studio Series Preamplifier and all is good except I cannot get the IR remote control to work. The micro is working since the dry contact inputs work and the unit steps through the LEDs when in set-up mode.
I have put a CRO on pin 2 of the processor and the demodulated IR pulses are present and at a good level. I have used the exact remote as described in the April 2006 article.
I am beginning to think that the crystal is not running at 4MHz however I can’t get a conclusive reading off the crystal (pins 4 & 5). Any ideas of how I can figure this out from here? (M. S., via email).
If this doesn’t happen then the remote has not been received correctly and the receiver will not respond.
If the crystal is incorrect in its frequency, the LEDs will not
respond in the set-up. Crystal frequency measurement must be made with a
impedance low-capacitance probe. Use an oscilloscope probe on a 10:1 setting.
I found a "Circuit Notebook" item in the January 2006 edition for a pushbutton relay selector. Could this circuit be modified so that it does not turn one relay off before activating the next (ie, so that it gives the option of multiple "lives"?). (D. M., Camden, NSW).
For example, in order to have both relay 1 and relay 2 on together, you’d need to have an additional selector pushbutton switch connected between (say) IC2’s output 5 (pin 1) and pin 9 of IC1c, to create a fifth (1+2) selection setting. Then you would also use a pair of 1N4148 diodes to connect between the O5 output of IC2 and the gates of Q1 and Q2, with a 100W resistor in series with each diode.
Then when you pressed S6, the extra selector button, the counter would stop at the O5 position and both relay drivers Q1 and Q2 would be turned on together.
Is it possible to check a capacitor discharge ignition for faults with just a multimeter? (K. W., Maryborough, Vic).
With the CDI powered up, test the high voltage supply which should be at around 300VDC if it has an inverter (ie, similar to our Multi-Spark CDI described in the September 1997 issue). If the high voltage is from a coil in the generator (see SILICON CHIP, May 2008), you should get some voltage when the motor is turned over. A typical figure would be about 50VDC on a multimeter.
You should then discharge the capacitor, using a 1MW resistor connected with insulated probes to the capacitor leads. Once discharged, check the voltage again before touching the CDI.
Next, check the SCR. Measure between the anode and cathode for a resistance greater than 100kW. Applying +5V to the gate input via a 100W resistor (and the 0V supply to ground) should cause the anode-to-cathode resistance to drop to a low resistance (less than 10W).
If all tests prove OK, then the CDI should work.
Shouldn’t the Minispot oscillator (SILICON CHIP, January 2008) have some way of attenuating the output level, so as to not overload the input to the IF stage, causing AGC to cut in and incorrect alignment to occur?
Would you use a pot? If so, what size and how should it be connected? We are talking about a high impedance circuit. (J. L., via email).
There is no easy way to add an attenuator.
I am trying to gather together all of the components for the prescaler project designed by Jim Rowe (October 2006). The ADCH-80 A wideband RF choke and the MC10EL35 JK flipflop do not seem to be readily available.
Do you have any suggestions for sources of supply or alternative parts? (N. M., Mt Pleasant, Qld).
The MC10EL35 and other On Semi-
conductor ECL devices should be available from Future Electronics Phone (07) 3886 4933 or www.futureelectronics.com
When watching many prime-time TV programs I prefer to mute the sound and rely on the subtitles available on Teletext page 801. This is because I often cannot distinguish the words from the foreground music. But I cannot find any way of recording the program to retain these subtitles.
I tried a set-top box which claimed compatibility with Teletext and it was OK for direct reception but not for recording. I also tried recording from the "TV out" sockets of a TV set which had this feature but again with no success. I asked several suppliers but the most useful answer I got was: "that’s a good question". Can anyone do better? (R. S., Armidale, NSW).
We put your question to Alan Hughes, who wrote the recent series of on digital TV. This is his answer:
No videocassette machine is capable of recording teletext subtitles in their undecoded form. The reason the VCR cannot record teletext is that the luminance channel of a VCR is up to 3.1MHz where as the teletext needs the full 5MHz.
The solution is to use a Personal Video Recorder (PVR) which will only record digital TV broadcasts. So in Armidale, NSW, you will be able to record all stations except NBN (but all stations in Armadale, WA). The PVR will have a choice on whether to record the subtitles and on playback you can choose to watch them or not. Check the menus in the shop . It will be in the installation menu. Then try it.
Notes & Errata
ds/PIC Programmer, May 2008: in the May 2008 issue (p67) describing the dsPIC/PIC Programmer, we explained that the MCLR-bar/VPP line was deliberately switched between 0V and +13V. This was done to avoid possible damage to the microcontroller when it is in the ZIF socket.
However, if you wish to use the external programming header (CON3) with a microcontroller on a breadboard, for example, you should connect pin 1 of CON3 (the MCLR-bar/VPP line) as shown in the accompanying diagram, adding a resistor (R) and diode (D) to the breadboard.
The diode and resistor allow the microcontroller to run when the MCLR-bar/VPP line from the programmer is at 0V. There will be no possibility of damaging the microcontroller in this case as the microcontroller is accessed outside the ZIF socket. Hence the diode and resistor allow the microcontroller’s MCLR input pin to switch between VDD and VPP. This is more convenient while still developing the software.
The PGC, PGD and GND lines can be connected directly to the pins on the microcontroller, as explained in the article.
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