Sorry for the late replies. I'll try to cover what I can here.
The good news is TapTation will be back in the store shortly. Aron and I have worked something out that should remedy the shortage problems we have been having.
The +/-30% accuracy on the digital pots: One has to learn the politics involved in the way technical datasheets are written. The only specs that a company is held to with datasheets are the specs that they guarantee. You basically have to read in between the lines for the rest. They obviously do not want to guarantee the resistance accuracy so they quote a huge number to cover themselves of liability. I have worked with alot of digital pots and I have never seen one vary by 30%.
The 5% accuracy: This is the max variation of delay time between the positions of the digital pot. When a time is tapped in the TapTation will set the pot to the closest position to the that time under ideal conditions. Thus the largest gap between time entered and delay time will be the 5%.
Now I say "ideal conditions". There is alot that can make the circumstances less the ideal and most of them the TapTation itself cannot deal with. Variation in the Pt2399's clock, temperature stability, power supply drift, circuit layout, etc. will all contribute to the accuracy issue. Lets face facts about the PT23* series, it was never meant to be accurate. It is an IC family that aims to make it cheap and easy for manufactures to add audio delay be it toys, karaoke machines, and other cheap devices. We just happen to be able to use it of our delay needs and there is nothing wrong with that as it is cheap and easy to use which are important factors for DIY needs. They also IMHO sounds fairly good but to expect any level accuracy out these ICs is quite frankly unrealistic.
I do have some theories in how to make the TapTation more accurate but some of those ideas might end up creating more bulky circuits increase cost and error for the DIYer. If you need that kind of accuracy which would require more circuitry you might as well switch to a different technology. The TapTation is a "best shot" added feature for a device that was never meant to be accurate. Its fairly simple and fairly accurate as my testing showed. Mind you who really needs that kind of accuracy ? Its not like the note will ring long enough for the time discrepancy to matter.
i used the vero layout and my subdivisions don't match up with the tapped tempo. i didn't add the dbl time switch. i also didn't add the led for the scaled tempo. would either of those matter? this is for a rebote. do i need to disconnect the 1k from pin6 of the 2399 on the rebote? thanks
Yes remove the 1K. It would throw off the calibration.
I do have to stress that the TapTation is only setup for the 100K digital pot. Replacing it with the 50K will throw all the calibration off.
A calibration mode...hmmm. What would I be compensating against with a calibration mode ? The variation in the PT2399 ? The circuit layout ? I would have to do more testing to see how adjusting the time to resistance would affect the internal calibration that is already in place. I'll look into it later.
Andrew
