i just built a midibox64 with 2 joysticks and 12 rotary pots. no DIN, DOUT, or LCD.
i have uploaded the midibox64 app, and i can see midi data when i move a joystick, but it crashes soon after. the regulator gets very hot.
i used 1k pots, could this be the reason?
without the pots connected, i read about 4k resistance between +5 and ground. with the pots connected it goes down to 9 ohms! is this the parallel resistance or do i have a short somewhere?
thanks for any tips,
greg
hi
i used 1k pots, could this be the reason?
no
without the pots connected, i read about 4k resistance between +5 and ground. with the pots connected it goes down to 9 ohms! is this the parallel resistance or do i have a short somewhere?
yes it really seems like that:
-check that all the pots are connected correctly 1-GND 2-AIN 3-+5v
-check that all the pots are ok (1k between pin 1 and pin 3)
-check the cables: how do the pots connect to the AINs ?pictures?
-remember that 1k pots may work but it s not advised, 10k is the best option
simone
is it possible to measure the resistance while the pots are in circuit? if i measure between the end terminals, won’t i just get the same resistance i’m seeing between power and ground?
the pots are connected to the AIN with a ribbon cable.
thanks for the tips. i’m only using 1k pots because i had a bunch that were the perfect size.
is it possible to measure the resistance while the pots are in circuit? if i measure between the end terminals, won’t i just get the same resistance i’m seeing between power and ground?
yes it is possible although i don t understand why you want to measure the resistance between Vs and Vd
i assume you have changed the configuration of the app to host 16 AINs
does it crashes without the pots connected?
use your multimeter to back trace voltages between CORE and AIN and between AIN and pots
simone
yes it is possible although i don t understand why you want to measure the resistance between Vs and Vd
…
measuring this way was correct, and the result indicates a short somewhere. to find it, first check the with the ain module connected and no pots, then add 1 pot at a time and measure the same way. measuring v works too, but since you are overloading the vreg, better to test for short with ohmmeter or continuity tester
yes it is possible although i don t understand why you want to measure the resistance between Vs and Vd
because there is apparently a short between Vs and Vd. with pots connected i get 9 ohms resistance, with no pots i get 4k. my calculation of the parallel resistance of the pots should be 400 ohms. so how do i measure the resistance of one pot in circuit without just getting the total parallel resistance, which = the resistance btw vs and vd?
i assume you have changed the configuration of the app to host 16 AINs
no! how do i do that?
does it crashes without the pots connected?
i haven’t tried, but i can only tell that it crashes because i don’t see midi appearing at the pc. without the pots, i don’t know what to monitor.
thanks for your help.
ok, i disconnected the ground wire from all the pots. with no pots connected to the AIN module, i get 4k between Vs and Vd. with the first pot connected, i get 800 ohms. with the second pot connected, i get 460 ohms. as i connect the rest, it’s just going to go further and further down right? what’s wrong here?
oops, i was calculating parallel resistance wrong. 10 1k pots should be 100 ohms. i have 12 1k pots, 4 5k pots (joysticks), and the resistance without the pots connected is 4k. i believe this should = 76 ohms with all the pots connected.
i wish i just had some 10k pots to swap in.
Gzifcak-
That “number of pots” pref should be in the main.asm file in the batch of MB64 stuff (DEFAULT_NUMBER_POTS). You’ll need to change the number and recompile the app with MPASM or whatever.
George
…with the first pot connected, i get 800 ohms. with the second pot connected, i get 460 ohms. as i connect the rest, it’s just going to go further and further down right? what’s wrong here?
this is the normal series for 1k pots
parallel resistance for equal resistors is Rp = R/N, where N is the number of resistors in parallel.
this total is in parallel with 4k so = 1/(1/4000 + 1/Rp)
you should wind up with ~60 ohms in total with 16 (assuming the joysticks are also 1k)
with the first 5 pots connected i have a resistance between Vs and Vd of 230 ohms, and it seems to work fine without crashing. regulator doesn’t get hot. i guess i’ll just connect another five and check it again.
ok, seems fine with 10 pots connected. resistance btw Vs and Vd is now 120 ohms.
…i believe this should = 76 ohms with all the pots connected…
correct.
even better, this should result in less than 100mA total draw.
i think you are ok with only 12 1k pots, more would be no good though…
ok, seems fine with 10 pots connected. resistance btw Vs and Vd is now 120 ohms.
hmm could it be you had the joysticks wired wrong?
well i’ve got all the pots reconnected now, and it seems fine. all i did was remove the ground wire from all the pots, so the wiring hasn’t changed at all. there must’ve been some invisible bridge that i finally broke. i guess when all else fails, disconnect and reconnect.
thanks for all the tips. i’m psyched that it’s working!