tgergo
Junior Member
Posts: 59
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Post by tgergo on Dec 7, 2021 10:09:58 GMT
I started this thread about gate generation and it got to the point of thinking about possible implementations. So here we go DIY. Requirements: * gate is opened trigger pulse * gate stays open for the time set by a length parameter * length parameter should be voltage controlled * the primary purpose would be to send the gate signal to an envelope generator I added a Falstad export as a draft. I appreciate all feedback very much. |
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Post by keurslagerkurt on Dec 7, 2021 12:48:08 GMT
Nice! Happy to see you taking on the DIY option to make a Gate circuit. I think its def possible with basic parts and would make a great addition to the AE world. I'm right now trying to come up with an as simple as possible basic circuit that gives CV input & trigger in. I think you switched the trigger & threshold pins when changing to falstad, they are not the same as on some other diagrams sadly. I added a txt file already which gives the basic gate out with button push. Its only a small change from the one you posted.  circuit-20211207-1339.circuitjs.txt (760 B) |
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tgergo
Junior Member
Posts: 59
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Post by tgergo on Dec 7, 2021 15:02:56 GMT
What do you think about this?  Edit: thank you for the fix  |
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Post by keurslagerkurt on Dec 7, 2021 15:20:48 GMT
What do you think about this? <button disabled="" class="c-attachment-insert--linked o-btn--sm">Attachment Deleted</button> Edit: thank you for the fix Nice! Thats a good trigger input stage!  I managed to squeeze a decent working circuit out on falstad, but it was a bit harder than I initially expected. The pot that fixes gate length is not a pot that varies a voltage (i interpreted the schematic wrong the first time around), but it is a pot that controls current. More specifically the current that charges the capacitor, and thus the current that regulates the time it takes for the capacitor to reach 3.33V. When the cap reaches 3.33V, the discharge pin of 555 pulls it back to ground where it stays until the next input pulse. So, in order to add CV, we need to regulate the current with a voltage. Which is do-able in this case: we can alter the voltage source that feeds the current into the cap. Right now, this voltage source is fixed at 5V with the power supply line. But if we bring it to for example 4V, than the cap will take longer to charge because there is less current flowing. The tricky point is that the voltage can not go under 3.33V, otherwise the cap will of course never be able to reach >3.33V which is needed for the 555 to toggle off. So I used two opamps. First one is an inverting summing opamp, which sums the two inputs (in AE: pot + CV) together. Next opamp acts as a rescaling + offset + inverting opamp, which brings its output voltage from 3.33V - 5V. This opamp's output voltage feeds the capacitor a current through another pot. This last pot can be used to determine the min-max gate times. If this 100k pot is at its maximum resistance, the min gate is 1.1s, max gate time about 4s. If you want longer max gates, you could use a larger pot. (eg 1M yields 11s to 40s, it scale linear). I think there is one thing that might be an issue when one would test this IRL: in order to charge the cap sloooowly, the opamp voltage must be close to 3.33V (eg 3.34V), but always above. This might require some calibration or trimpots. I also am not sure how picky the 555 timers are about this 3.33V. Do some toggle at 3.29V already and others at 3.37V? I do not know and i've not yet checked the datasheet. Anyways, fun circuit to play around with, will certainly try to build it on breadboard at some point. Not that much components: one 555, one MCP6002, one transistor and some caps & resistors.  555GateGenerator.circuitjs 1.txt (2.14 KB) |
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Post by keurslagerkurt on Dec 7, 2021 16:35:23 GMT
Have just checked the NE555 datasheet and the spread on the needed threshold voltage is pretty massive. The 'standard' value is indeed around 3.3V, but threshold can be up to 4.2V. This means that, in order to not get stuck in an infinite gate situation, a trimmer pot would be necessary instead of the 15k pot above the second opamp.
Other 555 variants (like the TLC555) seem to have the same wide threshold voltage spread.
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tgergo
Junior Member
Posts: 59
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Post by tgergo on Dec 8, 2021 12:11:48 GMT
I'll have to study this a bit. I'll also watch the opamp video someone referenced as a good resource. I hope you find the project interesting and enjoyable. I really appreciate that you take so much time to work things out.
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Post by keurslagerkurt on Dec 8, 2021 14:26:08 GMT
I'll have to study this a bit. I'll also watch the opamp video someone referenced as a good resource. I hope you find the project interesting and enjoyable. I really appreciate that you take so much time to work things out. I find this very interesting and a lot of fun I started out just like you some two years ago, just trying to alter other's circuits on falstad & breadboard, and I still love the magic of analog electronics. To be fair, I think this gate generator would probably be easiest to tackle with a microprocessor like Arduino, attiny or Pi Pico. It would probably also be easier to give it more 'advanced' features with a digital chip (like probabilities, arbitrary long gates,..). But wheres the fun in that?? I love analog design, its like a complex puzzle with tons of different correct answers, but some are better than others of course.. The opamp video from EEV blog (i think youre talking about that one) is FANTASTIC. You'll see that op-amps in basic operation mode are less complex than it looks. For the summing configuration i use with the first opamp here, i suggest this video (after you've watched the other one): |
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