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| Portable Low Frequency square wave generator circuit - Solved - page 3 |
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| spec:
The OP requested a circuit and out of all the posts on this thread, there is only one circuit has been posted- guess which one. --- Quote from: Laszlo on January 26, 2019, 08:22:34 pm ---My question is whether anyone on this forum knows about a working circuit which I could utilize to build my little project. --- End quote --- |
| spec:
--- Quote from: Zero999 on January 31, 2019, 04:24:54 pm --- --- Quote from: spec on January 31, 2019, 03:40:43 pm ---What on earth is all this mark to space ratio stuff all about? The circuit as presented will meet the OPs requirement and that is it. There is no more to say. By the way the 555 is a CMOS type. --- End quote --- Except the mark space ratio will not be 50% at 1kHz, because the value of R1 is so low the on resistances of the 7555's internal MOSFETs will skew the duty cycle considerably. The output stage inside the 7555 is not perfect. The output transistors have asymmetrical on resistances. The high side transistor's resistance is between 1k and 150R and low side transistor's resistance between 143Ohm and 16Ohm, depending on the supply voltage to the 7555. The higher the supply voltage, the lower the on resistances. I worked out the resistances, using the figures given on the graphs on pages 6 and 7 of the datasheet. https://www.nxp.com/docs/en/data-sheet/ICM7555.pdf --- End quote --- Your missing some very important points. * The OP does not want an exact 1:1 mak-to space ratio so what figure are you using to justify your negative comments about the MS ratio? * You have made general and sweeping statements about the MS ratio with a few figures quoted but no complete calculations for the M/S ration * You have not taken into accout the end resistance of the 2M potentiometer which adds to the effective resistance seen by the C555 * And worst of all you have failed to realise that the 1k resistor is a stopper so that the lowest resistance possibly seen by the C555 output is defined. If you do the calculations you will find that oscillator reaches 1KHz (the highest frequency requirement) well before 1kHz is reached. |
| spec:
--- Quote from: soldar on February 01, 2019, 11:48:09 am --- --- Quote from: Zero999 on February 01, 2019, 11:13:34 am --- We tend to avoid posting complete circuits here, as it discourages people from thinking. It's often more helpful to post hints and little circuits which the original poster can put together, that way they gain a deeper understanding of how it works, rather than some soldering practice. --- End quote --- Let me expand on this. This is not a free service where people work for you for free and provide you with turnkey solutions. We are here to help and learn from each other. If you want a turnkey solution you can go hire some engineer and pay them the going rate. Furthermore, many requests are poorly defined, poorly presented and poorly explained or even contradictory. Often getting further clarification from the OP is a slow and painful process, somewhat like pulling teeth. We could be here presenting solutions for days only to have the OP disappear (often happens) or reject different solutions on different grounds (to complicated, too expensive, not fulfilling needs which were not mentioned before, etc). So we take what we are given and kick ideas around and learn from others' ideas and viewpoints. That is the way I see it. --- End quote --- :wtf: |
| spec:
--- Quote from: Zero999 on February 01, 2019, 11:13:34 am --- --- Quote from: spec on January 31, 2019, 03:33:05 pm ---One thing that surprises me is that no one has commented on the circuits effect on global warming. After all there is a whole 1W2 being dissipated in the output stage.:-DD --- End quote --- Good point. It's being powered from a small battery, so 1.2W of idle power consumption is a killer. --- End quote --- Your making this up. The OP said it could be mains powered. Besides which, 2W2 is no big deal, even for battery power. |
| soldar:
--- Quote from: spec on February 06, 2019, 04:06:55 pm --- It doesn't matter what you have done or what you are. That does not grant you the right to make derogatory unfounded statements about other peoples designs. Just for the record, I have been designing circuits since before the 555 was even thought of. In fact I had a 555 chip before they were released in the UK. --- End quote --- I have no idea what your problem is with me since all my posts in this thread have been cordial exchanges with Zero999 and I have not once in this thread addressed or responded to your posts or made any comment about them. I do not understand your attitude and I have no idea why you called me "presumptuous". I don't know if you are mistaking me with someone else from some other thread or what. I have made no comments on anything you have said in this thread or, as far as I can remember, in any other thread. I have reported your posts in the hope that you will just leave me alone. E.T.A: I see you also have a beef with Zero999. Are you sure it's us? Maybe you are just misinterpreting people's motives? Why the confrontational attitude? |
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