Hero999

It's oscillating. Does it sound like a high pitched whistle or a low frequency buzz or hum? Have you turned the volume down to the minimum setting?

It won't be completely invisible, some visible light will get through so you'll be able to see the filament dimly glowing red. I don't know, it depends on the type of camera, I'm no photography expert.

I don't know, I would guess 800nm to 1000nm. Look at the datasheet, ask the the manufacturer. A single AA cell could be used to light an LED but you'll need a boost converter. It depends on how you design the circuit, an IR LED powered by two AA cells won't necessarily be brighter than it would if it were powered from a single cell but it will last for longer. An incandescent lamp with an IR filter.

What's DSLR? IR remote control LEDs aren't that powerful, you'll need a lot of them to get 7W to 10W. 7W-10W is quite a lot of IR, certainly more than a 100W incandescent. Does it need to be continuous or is it a pulse, like a camera flash? Obviously an IR LED is much smaller than an AA cell and of course using two LEDs will make it brighter.

An FM receiver is very sensitive and can be overloaded by high powered signals so an attenuator is required to reduce the amplitude of the signal. Use a wireless transmitter, remove the antenna and connect it to the antenna jack via an attenuator and coaxial cable. There are FM transmitter ICs available. That sounds too expensive, you should be able to build a modulator for less than that. You can even buy stereo FM transmitters for much less than $40, you could easily wire one to the antenna jack in the manner described above and in my previous post. Also, I'm kind of worried that they might just be overlaying the signal from the headphone jack onto the signal from the antenna. That's how my wireless transmitter works. It just overlays the signal. It's not that simple, I suggest reading the frequency modulation article on Wikipedia. Does it have to be stereo? A simple mono FM transmitter can be built fairly cheaply using a few transistors. For stereo, you should use a specialist IC.

Connecting a 470R resistor in series with the speaker makes very little difference to the the current, it increases slightly to 29.8mA. I'm beginning to question whether it's actually possible to trim the current to between 25mA to 30mA because R9 is too sensitive: with it set to 1k54 the current drops to 21.9mA. I would say trim the current to between 15mA and 30mA - you'll probably need a multi-turn trimmer to do that. Varying R14 is not the answer, it will alter the gain and biasing. It sounds like one of the components are faulty or there's a poor solder joint somewhere. My guess is there's a problem with Q4, perhaps its gain is much lower than it should be? Try replacing it. Have you checked that R9 reads near 0R when its set to its lowest setting? Measure the following voltages: VBE of Q4 (voltage across R10), should be about 0.6V to 0.7V. VBE of Q3, should be about 0.6V to 0.7V. VBE of Q5 and Q6, both should be about 1.2V to 1.4V. I'll post the LTSpice file if you like.

R9 is 2k but 2k2 will do fine. I've simulated it in LTSpice and R9 is very sensitive, with it set to 1k5 the current is 18.9mA and when it's set to 1k6 the current is 29.6mA. I haven't tested the cross over distortion yet and I've substituted some of the transistors as I don't have the models for all of them.

Please expand further audioguru. A rheostat and variable resistor are the same thing. He appears to have connected up the resistors correctly.

You shouldn't need to vary the value of R10. Do you understand how the biasing of Q5 and Q6 works? The voltage across Q4 needs to be equal to the VBE of Q5+Q6. The voltage across Q4 can be calculated using the following formula: VCE = VBE

It's not a case of digital or analogue, both the headphone and antenna jack are analogue. The headphone jack output is audio frequency and is a direct electrical copy of the sound wave, the antenna socket is VHF (Very High Frequency, assuming it's FM), frequency modulation. You need an FM modulator to connect the headphone jack to the antenna socket: an FM transmitter is an FM modulator. If you don't want to transmit the signal through the air, you can connect the transmitter to the antenna jack via an attenuator (just a couple of resistors) and coaxial cable.

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Yes, you definitely need a better/hotter iron.

How are we supposed to know what project you're building without the schematic?

It depends on what you mean by test the circuit board? If you want to ensure that the PCB is as per the schematic then use CAD software which creates the PCB from the netlist and performs design rule checks for you e.g. Eagle or DXP. If you want to check circuit functionality you can get simulation software for free - most people here use LTSpice which if freeware..

You need a 30V transformer. C1 needs to be at least 6800μF, preferably 10,000μF for 30V@3A out.

Yes, you can use a transformer, it just has to be decent. quality. I don't know whether your transformer has been manufactured to a high enough standard to be safe. Did you buy it from a reputable supply?

The resistor will cut the power delivered to the speaker and reduce the sound quality, you might as well build a small amplifier with a 0.5W speaker, four AA cells and an LM386 if you want it to sound like a clock radio. Changing R14 for an incorrect value will not help. There is an error somewhere else, check: the PCB, that all the components are soldered in the right places, the solder joints are all good and that the transistors all all good..

Assuming. a 30V transformer, a regulator drop out of 6.4V (going from what you said), a rectifier loss of 2V and an output voltage of 30V with a 3A load, I calculate the minimum filter capacitance to be 6521

Have you heard the element turn off again? If so it means that the thermostat doesn't have a high enough heat setting.

The LED should not flash, it should be continuously lit but it's normal for it to remain lit for a couple of seconds after the power is removed, as the filter capacitor discharges. Where is the 470R resistor? What do you mean by in front of the speaker? Do you mean in series? If so, it's not surprising the sound quality is poor due to the poop damping factor. It will be very quiet as the power will be only a few mW.

Just check the transformer is modern and has all the approvals required for your jurisdiction; in which case it will be isolated.

Yes of course you can just a transformer with the appropriate power rating. If the transformer provides sufficient isolation, 24VAC is pretty safe.

If that's as hot as your iron can get then you need to get a hotter iron. I was going to suggest that you check the voltage of the mains but the fact that the temperature is reaching 167

If you used the 74HC132 (note the different pin-out), as well as the OP290, the whole circuit will work down to 2V, enabling you to be able to run it from two AA cells.