Posts Tagged ‘LDR’

I dug out the Barefoot EXP LDR expression pedal I built sometime ago now from underneath the stairs to test some features on the Nova System. My Zoom FP02 has a 250k log pot inside it, which just doesn’t sit well with the Nova. Due to the Nova being able to be calibrated to the expression pedal the Barefoot suddenly becomes very useable even in below average light conditions. Here’s a demo of the Novas whammy, set to 2 octaves up.

And before you ask, the dog is called Bruce, he is a 9 month old boxer, and he appears to like guitar FX!

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If I made a mini version of the Solar Lifeforce without the CV mode and buffer on a toggle (the circuit would be buffered but the pedal true bypass) is that something you guys would want? When I say mini I mean really tiny – Hammond 1590A tiny like the Morse Device, Bomb Idea and 072 buffer. I think the description ‘volume and treble killer’ is more accurate than LDR volume pedal, but it can also act as a sort of foot operated tremolo. Price point would be around £40, and it would have a sticker decal (see below), not sprayed.

Here’s a link to the big old version in action, functionality, other than perviously mentioned, would be the same.

So, please vote so I can get an idea of how popular this idea would be if I were to make a small batch!

*Update 18/06/2012 – As the results of the above poll show there is no great interest in this pedal, so it is looking unlikely I’ll be putting it together as a batch.

So, here is a simplified schematic for the Solar Lifeforce. Basically I have removed the expression/CV out stuff, removed the toggle for the buffer so the buffer is always on, and made it as simple as possible. It could maybe do with some small value caps between both R5 and ground and R9 and ground, but they aren’t essential. The LDR is a pretty unreliable thing for any consistent readings so maybe buy a bunch and try them out until you find one that suits you, I have tried the circuit with ones of varying specs and they all have behaved OK. The best I found was on doctor tweeks website which can be found here. It has a dark resistance of 20M which is plenty, 10 lux (‘room’ light) resistance is between 50k-100k and it has a rise time of 20ms and a decay time of 30ms.

Before I go into the circuit I will warn you – LDR’s aren’t perfect for cutting volume alone as they roll off treble, so your tone will be altered. This isn’t a problem so much when you are playing in really well-lit conditions but it does become noticeable when you are in stage type conditions. Of course this may be what you want, but if you are after a ‘transparent’ volume cut a LDR is not the way to go.

Anyway, here’s the circuit. I havent included the LED/switch wiring etc in this one, and I haven’t put in reverse polarity protection. It is up to you if you think it is needed. If you think it is you could just use a diode such as a 1N4001 in series with the 9v rail.

R1 is a pull down resistor to help prevent popping when the circuit is bypassed/engaged. R2, R3 and C1 form the network which establishes the reference voltage for the op-amp. The first side of the op-amp acts as a buffer, and the second side acts as a gain allowing you to increase the volume to compensate for poor lighting conditions. VR1 controls the range of the LDR between being covered and uncovered and R5 sets the minimum for this. R9 and R10 set the gain of the b side of the op-amp, which is around 5  (G = 1 + (R10/R9) = 5.545), which is then attenuated by VR2 just before the output. C4 stops any DC leaking from the circuit into your amp. You could use a lot of different op-amps for this circuit. I used a TL072 because I like them, have a few kicking around and is a dual op-amp so takes up less room than two signals. They are also pretty cheap and quiet so are good for this kind of work. On the Barefoot which was really the predecessor to the Solar Lifeforce I used DPDT toggle switch to change between if the signal kills when the LDR is covered or is restored there, you could probably mod this circuit to include it. You could also use a DPDT toggle to cut the buffer out of the circuit if you wanted too easily enough. I wired the original so the buffer was independent of the pedals bypass, so the signal hit the buffer, then the bypass, then the rest of the circuit, but you could wire it after the bypass so that you have a switchable buffer aswell. Just to clarify on this diagram the buffer is always in the circuit.

Here’s the part list:

R1         1M
R2         10k
R3         10k
R4         1M
R5         10k
R6         LDR
R7         10k
R8         1M
R9         2.2k
R10        10k

C1         10uF
C2         100nF
C3         10uF
C4         10uF
J1         Input
J2         Output
U1         TL072
VR1        500k Lin
VR2        10k Log

I found the best way of mounting those odd shaped LDR’s that are specified as 5mm diameter but aren’t actually round is to use a 5mm bezel mount. And be sure no light can get to it from inside the enclosure from the LED!

Update 12/07/12:

The circuit above is a little crude in places, it is a barebones version of the hand drawn circuit I drew when experimenting with it. Perhaps a nicer version would be to have a gain control directly controlling the gain of the b side of the op amp (ala the MXR Distortion+) and a separate volume control as the gain pot is wired in this circuit in this circuit. That way you are not boosting the signal only to attenuate it.  The volume control is then completely optional as in many ways the gain will act as a kind of volume control anyway. Here is my revised circuit with the aforementioned mod, a few additional caps and a resistor to help cut out the really high frequencies before the buffer. Probably still a fair bit of room for improvement, but here we go! I haven’t built this version yet, but it should be OK.

Update 11/12/12:

I’ve modded this circuit again (haven’t tested it but thought I would post anyway, so beware!) to have some basic filtering on the power supply, set the output impedance at 1k and also adjusted the values of a few components to make them a bit more sensible. If you build this and can verify it works well please let me know!

Solar Lifeforce Revised Schematic

 

Solar Lifeforce Revision

Posted: February 28, 2012 in FX, Solar Lifeforce
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Here’s the revised version of the Solar Lifeforce. I may produce a very small number of these (maybe 2 or 3) if there is a demand, £50 delivered in the UK. If you’re interested in buying one email me at ben@0xdfx.com

Solar Lifeforce Order Update

Posted: February 24, 2012 in FX, Solar Lifeforce
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After a week or so of playing with the Solar Lifeforce I have decided that if I make any to order then they won’t have CV mode. Removing it allows me to simplify the design, reducing the costs and removing a semi-useful feature that most will never use anyway. So, if it does see the light of day (no pun intended!) it will be with a minor redesign to remove that feature. I will probably use different hardware to make it more user-friendly with the space removing the CV mode will give me. I will probably increase the amount of gain on tap as well, maybe x7 or x8 rather than x5, just incase.

If there is any interest for this please email me at ben@0xdfx.com and I will see what I can do. Price would be around £50, but remember you do get a high quality 072 buffer.

Solar Lifeforce Demo

Posted: February 21, 2012 in FX, Solar Lifeforce
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Here’s a quick demo of the Solar Lifeforce in some pretty awful conditions. The lights were so low that I had to use YouTube’s light enhancement +4 to make everything visible. The LED is actually purple. In better light conditions this pedal behaves much better, but obviously good light conditions aren’t something a playing musician can guarantee. Because the pedal is propped up rather than laying flat the LDR is always in partial shade, so again, conditions weren’t optimal. I’ll get that CV mode up and running at some point and demo that with the good old Geiger Counter…

The Solar Lifeforce LDR volume pedal is kind of finished. The line mode works perfectly, the buffer is great, but I’m having a few issues with the CV mode. Probably something simple, I’ll get that going too when I get a chance. Anyway here she is. It’s funny, it’s the pedal I have taken the most time over the looks and it its the one I like the least…