Customer:
I’ve connected a NOVA + I/O Expander with L298N to use PWM. The I/O Expander works great! The PWM pins on the NOVA are 14 and 16 (I also tried 13 and 12 but got the same result), and the IN1, IN2, IN3, IN4 pins are connected to I/O Expander pins 3, 4, 5, 6.
The problem is that when I write analogWrite 255 to both motors powered by a 3S Li-Ion battery, usually only one motor starts and it runs quite slowly. Sometimes the second motor starts too but that’s rare. When I bypass PWM and use jumpers instead, both motors spin like crazy (not slow like with analogWrite), so PWM would be useful to slow them down.
Here’s the confusing part: when I switch everything to a Croduino board, it works exactly as it should. I thought the issue might be the 3.3V, but I see online that the same H-bridge is used with RPi and according to the datasheet 3.3V shouldn’t cause a problem.
Is there something different about the PWM signal on the NOVA? Do I need to enable it differently than on the Croduino? Or maybe disable MOSI/MISO since I used those pins? If that’s even possible. I can’t think of anything else that could be the reason.
I’m not certain, but when the PWM was on pin 13, I seem to remember the LED staying constantly lit. It seems like on the NOVA the LED turns on with LOW, which would mean it was constantly LOW and that’s why one motor wasn’t moving. I’ll try putting a standard LED and test again.
Also, I have a quick question about the Amp+Voltmeter (INA219). I connected it in series between the battery and the NOVA. Looking from the battery: battery + pole to VIN+, VIN- to the + pole of the KIS3R33S regulator, and battery - pole to the regulator - pole. This all works great. The question is: can I use the INA219 to measure battery voltage without a load, meaning battery + pole goes to VIN+ and battery - pole to VIN-? That would mean the shunt in the INA219 is the only load. Is that allowed? It seems to me like it might not be, or maybe it’s allowed up to a certain voltage level until the current through the shunt becomes so high it damages it. I looked at the datasheet but I can’t quite figure it out, so information like “only use in series with a load” or “don’t measure battery voltage without a load” would be enough for me.
Original message (Croatian)
[name removed] bok!
Imam jednu situaciju koja mi ne radi dobro i možda mi je nešto promaknulo.
Spojio sam Novu+I/O Expander s L298N na način da mogu koristiti PWM. Inače, I/O Expander je genijalna stvar!
PWM pinovi na Novoj su 14 i 16 (probao sam i sa 13 i 12 ali je isto), dok su pinovi IN1,2,3,4 povezani na I/O Expander 3,4,5,6.
Problem je da kad dam analogWrite 255 na oba motora koji su napajani s 3S Li-Io pokrene su uglavnom samo jedan motor i to dosta sporo. Ponekad se pokrene i drugi ali je to rjeđa situacija. Kada maknem PWM i stavim jumpere, motori se vrte ko ludi (ne onako sporo kao s analogWrite), zato bi mi i pasao PWM da ih usporim.
E sad ide onaj dio koji me zbunjuje. Sve prebacim na Croduino i radi baš onako kako treba. Mislio sam da je problem u 3,3V ali vidim po netu da se isti H-bridge koristi i s RPI i prema datashetu 3,3V ne bi trebao stvarati problem.
Ima li nešto u PWM signalu kod Nove, tj. treba li ga eneblirati na nešto drugačiji način nego kod Croduina? Ili možda isključiti MOSI/MISO jer sam baš te pinove koristio? Ako se to uopće može. Ne pada mi ništa drugo na pamet što bi mogao biti razlog.
Nisam siguran, ali dok mi je PWM bio na 13-ci, kao da mi je ostalo u sjećanju da je LED-ica stalno svjetlila. Čini mi se da se ona kod Nove pali na LOW što bi značilo da je stalno bio LOW i zato mi se jedan motor nije pokretao. Probat ću staviti standardnu LEDicu pa ću onda probati.
I odmah da pitam nešto za Amp+Volmetar (INA219). Spojio sam ga u seriju između baterije i Nove. Gledajući od baterije: +pol baterije na VIN+, VIN- na +pol regulatora KIS3R33S, a – pol baterije na – pol regulatora. I to sve radi super. Pitanje glasi: smije li s INA219 mjeriti napon baterije bez trošila, odnosno da + pol baterije ide na VIN+, a – pol baterije na VIN-? To bi značilo da je shunt u INA219 jedino trošilo. Smije li to tako? Nekako mi se čini da ne smije, odnosno možda smije do neke razine napona dok struja kroz shunt ne postane tolika da ga ošteti. Gledao sam danasheet i ne snalazim se baš u njemu pa bi me zadovoljila informacija npr. smije se mjeriti jedino u seriji s trošilom, napon baterije bez trošila ne.
Originally submitted via email support on 10 February 2018. Migrated to the forum for community visibility.
