New Looper Design

slacker · February 02, 2006, 08:37:44 AM

I've ordered the chip for this. My plan is initially to put something simple together just to see if the switching scheme works, then move on from there. I'll post results as soon as I've got some.

Jaicen_solo · February 02, 2006, 08:43:16 AM

I'm going to go get the chips for mine this afternoon if they have any in stock.
Hopefully I can finally get this damn thing built!!

slacker · February 03, 2006, 04:04:30 PM

I've got a stripped down version hooked up on my breadboard. At this stage I haven't bothered with the analogue side of things I've just got an opamp buffer on the ana in and Sp+ for input and output. Unfortunately unless I've missread the schematic and wired it up wrong the switching doesn't work. It is entirely possibly I've got the theory behind the switching wrong so here's what I think is supposed to happen.
PD is low to enable the chip, if PR is high it will play back until you put PR low when it should record then putting PR high again plays back what you've just recorded.
Unfortunately simply switching the state of PR doesn't work. If it's playing and I put PR low it just stops playing, if it's recording and I put PR high then it carries on recording. The only way I can make it change what it's doing is to pulse PD high after I've changed the state of PR. For example if it's recording I have to put PR high then pulse PD high to make it start playback.
Like I said hopefully I've done something wrong or misunderstood the switching.
On the plus side it doesn't seem to pop coming out of a powered down state and the sound quality's pretty good .

Jaicen_solo · February 03, 2006, 06:25:12 PM

Thanks Slacker, I guess I let the switching scheme get away from me somewhat. I think you do have the theory correct, unless i've forgotten something.
As it stands, I think you'll probably need three switches if you want true bypass. Originally i'd planned to wire Play/Record to one half of a DPDT switch, with the second half wired to the reset pins. Connect the center of the reset pin to a 100K resistor to ground, and the two contacts to Vcc. If the switch is a break-before-make type this might allow PD to be pulsed enough to reset, restarting playback. If not, I guess you'd need to have a bypass switch and a reset switch.
To be honest, I'm confused as to how Zach's design is able to record whilst in the bypass mode if it's still true bypass. I can't see how it's done with just two switches.

I'm not entirely sure why the chip doesn't immediately begin playing when switching P/R from low to high. According to the datasheets that's all it needs, however you could try adding the indicator LED's and transistors connected to the P/R and EOM pins. I have a feeling this might provide a low going pulse to reset the state once recording is finished.
I'll do a little more research and let you know tomorrow, i'm a bit rusty on right now.
BTW, I had to order my chip online as my local maplin didn't stock the 2560, surprise surprise, so that's put back my efforts somewhat.

slacker · February 03, 2006, 07:01:39 PM

Quote from: Jaicen_solo on February 03, 2006, 06:25:12 PM
Thanks Slacker, I guess I let the switching scheme get away from me somewhat. I think you do have the theory correct, unless i've forgotten something.
Connect the center of the reset pin to a 100K resistor to ground, and the two contacts to Vcc. If the switch is a break-before-make type this might allow PD to be pulsed enough to reset, restarting playback.

Yeah I'd had that thought I'll give it a try.

Quote
To be honest, I'm confused as to how Zach's design is able to record whilst in the bypass mode if it's still true bypass. I can't see how it's done with just two switches.

It's not true bypass, the mod to allow recording in bypass mode basically leaves the input connected when bypassed, it's explained somewhere on his site. Presumably the pedal doesn't stop looping when you bypass it.

I'll try hooking up the LEDs and see if that helps. If not I'll try and figure out how to trigger a pulse, shouldn't be too hard and the design will still be simpler than the dirty sam.

Jaicen_solo · February 03, 2006, 08:55:31 PM

It also occured to me that you might have it configured in the wrong operational mode. Are you following the digital schem posted here? If not, which address pins are going to ground??

slacker · February 05, 2006, 09:40:09 AM

yeah I've got the address/mode pins connected like in your digital schematic.

slacker · February 06, 2006, 04:23:23 PM

well I played around with this all day yesterday, nursing a hangover I might add, and I've come up with a switching solution that works. It uses a couple of gates of a 40106 to pulse the PD pin and one to select play/record, just to debounce the switch. It's fairly simple and the other gates can be used to switch the LEDs. If no one has any luck with a switch only method I'll post a schematic.

robbiemcm · February 22, 2006, 06:48:59 PM

Slacker: how did this turn out for you? Do you think there could be a chance of some audio clips if you get the chance

Thanks in advance,
Robbie

slacker · February 23, 2006, 08:07:59 AM

It's still on breadboard at the minute, because I was waiting to see if Jaicen_solo had any luck getting his original system to work. The switching I've done works fine but I'm still playing with the audio side of things. I'll post my switching schematic and try and do some sound clips.

robbiemcm · February 25, 2006, 11:15:50 AM

Slacker: with the switching scheme you are using, can you do it with only 2 switches or do you need a third?

bond · February 26, 2006, 04:01:09 AM

bump

any progress anyone?

slacker · February 26, 2006, 07:11:05 AM

Quote from: robbiemcm on February 25, 2006, 11:15:50 AM
Slacker: with the switching scheme you are using, can you do it with only 2 switches or do you need a third?

It works with 2 switches same as Jaicen's design. One of them is a true bypass that also resets the loop to the start when you engage the pedal. The other switch is play/record.
Heres the play/record switching schematic, like I said it's still a work in progress but it works.

Jaicen_solo · February 26, 2006, 07:27:47 AM

Slacker, that's a really neat and elegant solution to the switching problem. I'm thinking that a layout for that should be included with the project files as a daughterboard, or maybe even integrated into the existing layout since it's only a single 14-pin dip that shouldn't be too hard.

slacker · February 26, 2006, 07:42:39 AM

cheers, feel free to add it to the project files. I've got no PCB design software, I'm strictly a vero man, so I'm afraid I can't help you out with layouts.
I take it you haven't managed to get the switch only method to work then?

bond · February 27, 2006, 04:48:45 AM

mmmm i'm gonna order the parts an the 40106 chip, and breadboard it and try get it to work...

bond · February 27, 2006, 10:41:57 PM

why is ther a LDR on the board?

Jaicen_solo · February 28, 2006, 07:27:25 AM

The LDR is used to vary the supply voltage going to the chip. It's a bit of a dirty hack but it should allow for some vibrato. Using the values I've calculated gives the maximum swing in voltage between min and max.
I'm starting to feel like an absent father to this project a bit. I really haven't had time to get anything together lately. Many thanks to Slacker and all those that have kept this thread alive.

robbiemcm · March 01, 2006, 11:30:59 AM

Heh, don't worry I'm sure I'll be keeping it alive until I decide I can safely start my project, then drive you mad wondering why the hell it doesn't work.

Jaicen_solo · March 01, 2006, 11:38:16 AM

Thanks Robbie!
It just occured to me that i'd originally designed the LDR to be paired with an LED driven from a 40106 oscillator. The oscillator's not my design it's from Tim's PWM design, but I think i'll resurrect it to use up the remaining invertors from the switching schem!

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New Looper Design