Hero999

A photodiode/transistor with a red filter?

Lol, I've never heard of a radio controlled egg. ;D Remote controlled toys normally use 27MHz or 433MHz because they don't require a licence. I doubt they use anything as complex as rolling code like a keyless car, it's probably much simpler.

You shouldn't need a protection circuit. Just ensure the adaptor can provide enough current and its voltage rating is high enough to power all the LEDs. You still haven't said what their voltage drop is. If you don't know, it can be guessed from the colour: infrared are below 1.2V to 1.6V, red and orange LEDs are about 1.7V to 2V, yellow and yellowish green is 2V to 2.4V, pure green, blue, violet, pink and white are around 3.5V.

Audio isolation transformers are used to prevent ground loops. I don't know whether that will be a problem here because you haven't provided enough information about the equipment. Are all the appliances double insulated? Do they have two core or three core mains cable?

What comparator ICs are you using? With the circuit as you've drawn it, you need a device which can source current, most comparator ICs such as the LM339 have open collector outputs which can only sink current.

It also sounds like you're trying to use an RF transformer. I don't see any need for an isolation transformer, just connect the chassis together and the inputs to the outputs.

The comparator will turn on when the voltage at the + input exceeds 5V. You need to rearrange the potential divider formula. http://en.wikipedia.org/wiki/Potential_divider It can be a bit of a fiddle to calculate resistor values that are standard values. It's also a good idea to add a high value resistor from the output to the positive input to provide hysteresis which will prevent oscillation when the voltage is near the threshold.

How did you know that? Assuming what you've said is true, it's only part of the kit and is incomplete. The real kit probably has a couple of RF stages after the part shown here and possible pre-emphasis.

It's total nonsense. It's probably been translated into English from another language using software rather than human brain. A radio frequency choke is normally just an inductor with a high impedance at the freqency of interest, try a 4.7

Please post links iwhen asking questions in future, didn't you read the sticky? I assume you're talking about the projects linked below: 1) http://www.electronics-lab.com/projects/misc/014/index.html 2) http://www.electronics-lab.com/projects/misc/015/index.html Number 2 won't work because a CMOS NAND gate can't output enough current to draw a relay. Number 1 uses a 555 timer which can be configured to give a <50ms delay but it might not work with a relay because the contacts will take a finite time to open or close.

Please post the schematic. If you want to connect 1000 LEDs drawing 30mA each in parallel you need a 30A power supply. What's the forward voltage of the LEDs? Connecting them in parallel is wasteful, you should connect as many in series as possible, for example if they're red LEDs and have a forward voltage of 2V you could connect them in 200 strings of 5 connected in series which would reduce the current requirement to 6A.

What problem would that be? The only problem I'm aware of is the spectral response of the detector and I've already said how to fix it. From a functional point of view it doesn't matter whether you use three detectors and one LED or three LEDs and one detector, both are equal. My colour scanner uses a monochrome image sensor and three LEDs strobed because it's cheaper than using a white LED and a colour sensor. The light appears white but you can see a rainbow effect at the edge of the lamp as it moves down the page. If your using a microcontroller then it's probably easier to use three LEDs because the whole thing can be interfaced with using just three I/O pins but you can't turn all the LEDs off.

The unregulated circuit in my previous post is based on the same topology as the circuits in the post before it. The two regulated circuits I posted both work on the same principle: the output transistor turns on, as the current in the coil builds the voltage across the sense resistor exceeds a certain threshold, set by either a comparator or the conduction voltage of a base-emitter transistor junction, the output transistor turns off for a time determined by an RC time constant and the cycle repeats. Here's an article which describes how the comparator circuit I posted works, see page 38. http://ww1.microchip.com/downloads/en/DeviceDoc/41215C.pdf You could use a discrete comparator if you like but it needs to be push-pull, if it's not i.e. it's LM311, LM393, use the circuit with a comparator above. Note that the circuit contains an error: the +/- inputs are the wrong way round.

You're half way there. You need an inductor, not a capacitor if you're going to do that. The value will depend on the switching frequency, input voltage, LED voltage, current and maximum acceptable current ripple. It's true that the current will vary depending on the input voltage but that might not be a problem. This circuit is the switch mode equivalent of just using a resistor but it's well worth it as it's much more efficient.

Then an isolation transformer is not necessary as long as all parts have class 2 insulation from the user i.e. there's no chance of the insulation failing resulting in an electrocution. See the Wikipedia article: http://en.wikipedia.org/wiki/Double_insulation Yes, if an isolation transformer is used the fuse should be before the transformer, to prevent the cable from overheating if a short circuit develops in the primary. Is depends on how well the metal parts are insulated from the live circuitry: it goes back to the question of double insulation. If you're unsure, then connect all metal parts to earth. This only applies when no isolation transformer is used. If you're using an isolation transformer then there isn't any need to earth any of the metal parts as long as they're double insulated from the primary side of the transformer. The only thing you should ensure is that if the metal parts only have single insulation from the transformer's secondary, you should electrically bond them to each other. This is to ensure they're all at the same voltage i.e. if the insulation fails there's no chance of one plate being at 0V and the other at 230V. No, is the short answer. If no isolation transformer is used, connecting the DC side to earth would at worst blow the rectifier, at best cause the earth leakage breaker on your building's distribution board to trip. The earth is electrically the same connection as the neutral: look at the circuit and predict what will happen if you connect the neutral to the circuit's 0V rail. If you are using an isolation transformer then nothing bad will happen but connecting the 0V to earth would defeat the whole purpose of using an isolation transformer.

It was along time ago, about 15 years. I think that was also wrong, the big bit was positive and the small bit negative.

I bought some over priced LEDs from Tandy (the now defunct UK branch of RadioShack) which were backwards: the long lead was the cathode and the short lead the anode which could explain this. Here's my suggestion. I'm going to assume that you've already connected the LED the right way round, otherwise it wouldn't be working. All you need to do is connect R1 from the NOT gate to the transistor's base.

One of the resistors could be replaced with a potentiometer to adjust the temperature threshold.

Thermocouples are accurate but not simple to use. I'd recommend a simple thermistor. You don't need a micro-controller, a simple comparator and relay will do. http://www.silicontronics.com/index.php?action=ezportal;sa=page;p=17

Great, it's good that you've returned. I didn't make much effort to respond in case you didn't return: many people don't. English is the main language spoken on this forum. I'm from England myself but there are plenty of people here from all around the world. I know there is a Filipino forum similar to this and I think some posters confuse this forum with it. You could use three photo diodes with red, green and blue filters on them and a single white LED but it's probably better to use three LEDs and one photo diode. The idea, is you flash each LED on briefly at a high frequency and monitor the reflected light with the photo diode. You can sense the colour by monitoring the amount or red, green and blue reflected. Photo diodes tend to be more sensitive to longer wavelengths (i.e they're better at detecting red than blue) so you'll need to compensate for that whether by using software or making the green and blue LEDs brighter than the red LED. You can buy LEDs with red, green and blue LEDs in the same package which will save space and maybe even money.

Sorry but that still will not work as you've drawn it, a photo diode should be reverse biased. As you have it shown, current will flow through the LED and both blow it up and the transistor. To use it in photovoltaic mode you need to connect it between the base and emitter. Don't you mean you used an LDR not a photodiode? You're right about not requiring a pull-up for TTL, although it is a good idea. I need to be sure you have the circuit correctly drawn before I can help you with the bouncing. How many spare inverters do you have on the 7404?

Asking the same question more than once does not increase your chance of a helpful response but only reduces it as people get annoyed at having to read the same thing over and over. Seriously, if I asked you the same question three times would your answer be any different the third time round? No, unless you count saying you've already told me twice, go away! If no one responds, it could be because you haven't provided enough information so you could add another post to the same thread giving more detail. Be patient; give it a few days at least before bumping the thread. There again there is the chance that no one on the forum knows the answer to your question, sorry we don't know everything. Just be clear that creating duplicate threads will be treated as spamming and repeat offenders will be banned.

Whilst that would work I think it's a bit overkill. If the transistor is connected up correctly, a high value resistor connected between the base and the output of the NOT gate will provide positive feedback and therefore hysteresis.

The circuit drawn wrong. The diode is connected backwards so a large current will flow both through it and the transistor's base causing them to both overheat. The emitter is connected to -5V when you probably meant 0V. There's no pull-up resistor on the input, I assume it's a CMOS input so can be susceptible to noise. I don't believe you have the circuit connected as shown, otherwise it wouldn't work. You probably have connected the diode the correct way round and the emitter to 0V. The problems you're having are due to the lack of a pull-up resistor and hysteresis.

Is this spam? What's the point of the poll? Loads of people could respond yes or no and you still wouldn't receive any help. Even if I knew someone, I wouldn't give their number or email to a stranger on the Internet. You've missed the whole point of a forum. The idea of an Internet forum is to ask for help and advice on-line, not via email or phone. Posting your phone number on the Internet is also a very bad idea.