Author Topic: Can a LDR/LED be constrained to only output resistance in specific range?  (Read 3295 times)

moid

Thread resurrection! I'm finally on holiday... well staying at home this Summer, but at least no work for a few weeks! OK Duck I have just removed the 47R resistor and swapped it for a 2K2 (socketed so I can try other values if required). The LED comes on but doesn't dim or fluctuate at all, regardless of what I set the pots to. Something isn't working in that circuit, so I think I'll now make vero version of a simpler circuit I've built on breadboard (which does work; on breadboard at least). I'll post the vero as soon as I've finished drawing it.
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moid



OK here's a vero and schematic of a circuit that does pulse - the schematic is fine, does the vero look OK to anyone? I will try to get building this later tonight once the rest of the family are asleep.
Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

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moid

... and I’m stupid; I forgot to add the LDR to the circuit! I will redraw later, sorry for wasting anyone’s time.
Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

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duck_arse

erm. ldr? that is part of the other circuit, isn't?
Now battery powered. Remove plug when not in use, please.

moid

Arrr now there you go Duck, mistaking me for someone who looks like he knows what he's doing! That would be sensible! Moi?

Well actually it's more that the original circuit was just the twin T filters (which works), and only afterwards did my brain conceive this wonderful plan of adding an autowah effect to it... so there's no room on the original vero for an LDR, so it has to go on the vero board for the pulsing LED thingamujig. At the moment, due to a (possible) miscalculation in the design of said LED blinky blink, some jumpers had to be added in a way that I suspect might bring tears to your eyes and a strong Australian oath to your lips... so I'll post it later (when it inevitably breaks) and you can say, see, that bit will never work, and why did you do it like that? In that polite but firm voice you reserve for dealing with children and wild animals*

And if by some minor miracle it works I will post it and show how I laugh in the face of well thought-out planning while somehow achieving my twisted goals (and sotto voce) "phew, blimey, that one actually worked! Hah, fooled them into thinking I know something!"

*I may have go with a plea of insanity. Or the devil made me do it. Whichever seems more believable. One of my threads is nothing but a rollercoaster ride of emotions. Never a dull day here folks. Bloody hell it's hot here, my brain was never designed to function at such extreme temperatures :(

Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

https://mushroomsinshampoo.bandcamp.com/album/summer-endings

moid

Ye gods it's even hotter than it was before! However some late night tinkering has resulted in (mostly) success :) I now have a functioning autowah sound that is quite musical (yay). But of course I have some questions... firstly how to make the LED blink circuit speed up a little? I thought slow would be best for the effect, but it turns out that fastest sounds better (slow does sound nice if whatever signal going in has a ton of sustain), but for less shoegaze / ambient passages, it would be great for the blink to happen quicker. Is that just a case of switching a different pot out? I suspect not because measuring the pot on lug 2 shows the fastest blinking happens when resistance is 0 ohms. SO... change a resistor in the circuit itself? Also (for those who are interested) a very bright blue LED gave a much better result than a normal green or red LED (which were very subtle).

Here's another odd question - the effect only works if I connect a cable from power jack ground to the LDR leg at D11 on the vero board (see also red writing / arrow in below) image. I've not drawn that onto the vero layout yes, just on the schematic part above. Does this mean I screwed something up in my vero layout? (I'm happy to just solder a cable from ground to the LDR as a fix, I just wondered if it was obvious what daft thing I've done).



Thanks for the suggestions; I hope it's cooler wherever you are!

Duck - please ignore the horrible use of a curved green jumper cable on the veroboard layout... I'd already cut the board out when I realised that I hadn't allowed for any space to connect the cables for power, ground etc... minor stuff I know, but the circuit seemed a little subtle or transparent without them :) (I blame the heat, or the current state of world fascism, or the lack of decent snacks in the kitchen at the moment... one of them is the cause of all the evils in the world I'm sure)
« Last Edit: August 10, 2020, 10:03:50 AM by moid »
Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

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duck_arse

NO! not cooler, bloody hell. it's freezing enough cold here, and you want it more so? bah!

also, no, I can't unsee curved green lines, that's a black mark against your name. I hope you know this will go down on your permanent record.

faster = 1uF or 4u7 or 10uF instead of that 100uF. easy.
Now battery powered. Remove plug when not in use, please.

11-90-an

The cap along with that 50k pot determines speed so when pot value’s lowest isn’t low enough, change the cap! 8)

Anyway, i do like looking at that shade of green jumper, so i believe duck should be slightly less harsh... ;)
flip flop flip flop flip

moid

NO! not cooler, bloody hell. it's freezing enough cold here, and you want it more so? bah!

also, no, I can't unsee curved green lines, that's a black mark against your name. I hope you know this will go down on your permanent record.

faster = 1uF or 4u7 or 10uF instead of that 100uF. easy.
I thought the land down under only had two temperatures? - damn hot and on fire? I'll take as much cold as you can send us, it's 33 degrees C here at the moment and we have another 4 days of this terror to get through... my body was not designed for such extremes... it's too hot to solder things :(

I'll make sure I scourge myself with tangled 6.35mm cables to atone for my sins! I'll never do it again! I promise! I'll make a final clean layout soon showing how it should be done in case anyone else feels the urge to recreate this circuit. And then ask the boy wonder if he'll play some fancy notes through it for your delight and delectation. Good lord, I might have to find an enclosure for this one!

Thanks for the cap info, it's strange how I thought that slower would be best... I'll try that 10uF first; the circuit doesn't need to go a lot faster, just a bit quicker, and I want to hang on to some of the longer swells it does (about 3.5 seconds at the moment which is a bit too long). I think I'll socket this one and try again. You'll have to wait a day or two for results; we're getting a dishwasher delivered and installed tomorrow (yay, no more washing up in the sink, hello the future!) so the kitchen (where I do all my soldering, naturally) is completely emptied so the delivery chaps can get in and install this magic box.


The cap along with that 50k pot determines speed so when pot value’s lowest isn’t low enough, change the cap! 8)

Anyway, i do like looking at that shade of green jumper, so i believe duck should be slightly less harsh... ;)

Thank you, I thought it was a lovely green too :) And it complements the flashing blue LED beautifully darling! And thanks for the advice about the capacitor, I was wondering how that effect could be achieved - so the relationship between the two parts controls the speed of the flash? So for slower I would use a larger pot size because that is easy to change, but for quicker I would reduce the capacitor - so is this similar to a passive low pass circuit RC circuit? To find the frequency the low pass starts at you use a combination of resistor and capacitor... to set a frequency, and that frequency is also a frequency that could be used to determine oscillation of the LED, but one that is much lower than audio frequencies! Blimey I *might* have just understood something!

I think Duck is trying (bless him!) to make something competent out of me...
Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

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moid

Yay! Success :) Thanks very much chaps! I made some changes to the circuit for better sounds (swapped that 100uF capacitor in the blinking LED section for a 22uf and a 4.7uF for faster rates after playing the pedal for a day) and we have a boxed and working Autowah :) For those of you who like technical pictures, see the schematic below. And for those who like a nice vero layout (with colours!) then the even more below image doesn't reflect exactly what I did (on the mess inside my pedal), but does reflect what I should've done! I'll try to get my son to record something good through it tomorrow so you can hear it.

There are two parts of the schematic drawing that I'm not sure about. The first is on the far right, where the LDR is, I added a line off that to ground (in the pedals this is soldered to one leg of the LDR). Without it the LED blinker refuses to work, yet it wasn't needed on the breadboard version... so no idea if it should be there in the drawing?

Second query is about how I've drawn the 100K lin pot on the left side of the schematic and how it connects to the SPDT. I'm pretty sure I've done it right (the vero layout shows an exact copy of what I did), I'm just not sure if that's what I've drawn on the schematic?





Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

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duck_arse

hurrah! I think you have made that 56k redundant - supply at one end and ground at the other, it's just using current now. snip-snip. but the added ground lead seems to be correct.
Now battery powered. Remove plug when not in use, please.

moid

Hi Duck - thanks! On the grounds that the circuit is working and it's boxed I'm not touching anything for fear of the magic smoke and tone fairies escaping :) Thank you for telling me though.
 
We made a demo (for those of you who want to hear this pedal because there aren't any demos of it on guitar that I could find) so feel free to laugh at my explanation of it :)

Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

https://mushroomsinshampoo.bandcamp.com/album/summer-endings

11-90-an

Hi Duck - thanks! On the grounds that the circuit is working and it's boxed I'm not touching anything for fear of the magic smoke and tone fairies escaping :) Thank you for telling me though.
 
We made a demo (for those of you who want to hear this pedal because there aren't any demos of it on guitar that I could find) so feel free to laugh at my explanation of it :)



Cool!
Your son is a good guitarist... you raised him (or taught him ;)) well.... :icon_biggrin:
I think that pedal should be called a “auto-nyah” rather than an autowah due to the sounds it creates... ;D
flip flop flip flop flip

moid

Thanks very much! My son taught himself; he is far better at playing than I am - he shows me how to play!

Auto nyah sounds like a fun name!
Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

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duck_arse

moidy - geeze, it gets busy at the end there. very wah-trem. never mind that, I think I've finally -scroll-scroll-scroll-SCROLL- worked out "the error". the wire on the ldr you added to ground should instead go to the emitter//10k of the filter transistor. and snip-snip the 56k, bosh. I think. if your built actually matches your drawn, obvs.
Now battery powered. Remove plug when not in use, please.

moid

Hi Duck, thanks for the thoughts -  I will try to draw out what I think you're telling me tomorrow - past couple of days have been tons of DIY to cope with due to the incredible rain we've had - over a month of rain in two days! (a gutter and drainpipe got wrecked, plus loads of other smaller problems). Hopefully I get some sleep tonight and can focus on what you've written tomorrow.
Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

https://mushroomsinshampoo.bandcamp.com/album/summer-endings

moid

OK Duck, the weather changed and now we have no more predicted rain for a few days (yay)... just after I finished fixing the last drainpipe, it stopped bloody raining. Someone's playing games with me...

I've revised my vero layout; is this what you mean? I assume the ground you mention was actually for the transistor on the blinking LED board and not the filter board though (because that transistor previously had nothing attached to the Emitter - oops), but yell if you really did mean to move it across to the other board. I removed the 56K resistor but have replaced it with a jumper (column 13) so that the power can get from the +9V to the LDR and 33K resistor. Does the below look any better? If so I'll re draw the schematic as well.

Mushrooms in Shampoo -  FINALLY A NEW ALBUM Summer Endings

https://mushroomsinshampoo.bandcamp.com/album/summer-endings

duck_arse

mmmmmm ...... no. that's not it.

as I see it - see the 100k pot connects the emitter to the cap//cap to select the thing range? I'm assuming you are aiming to have the swept element replace the pot, so it's like PRR's little devil turning the knob up and down. so all you need do is have one end the ldr on the emitter, and one end that pot on the emitter. the two free ends go to the switch, the switch common goes to cap//cap point.

then you could have constraining resistor across the ldr to limit it's max if you wanted, or you might be able [I keep trying to work this bit in my head] to wire the ldr across the pot ..... erm - but for the next build. if you're happy wit der zound now, leave it I'd say.

it's better to think of the ldr as part of the filter/tee section, and drag its symbol across there to the switch, and then "link" it to the led with some light arrows/lightning bolts - this will have you right thinking when circuit looking, and yule be less confusable about the whole thing.
Now battery powered. Remove plug when not in use, please.