Dear: LMR
Just to let you know I am hoping to make a pcb for my robot in hopes I am not going to need a new chassis. Is this schematic correct because I am not so sure about the USB, the regulators, and the crystall oscilator. Thank you.
From: Noah
Schematic
Observations:
- Insufficient capicators!!!
- Do the L298P require external diodes
- 7V from a 5 volt regulator?
- Reset looks wrong.
- L298P SENSE lines need to go to ground.
- What is the current load of the motors?
Which schematic capture / layout tool are you using? Can you use multiple pages to clear the clutter?
Thank you and here are some questions.
Dear: GG
First of all I am not sure if the capacitors are insufficient. How many farads should I use for the capacitors you say? The L298p from the documentation I’ve read doesn’t require any external diodes. Do you need to see it’s datasheet? Also how is the reset wrong and what should I do? Thank you I’ll put the sense lines to ground. The current load on the motors is 5 amps. That it does say on the pololu datasheet for the motors I am using. Thank you. Also I can’t use schematic capture as far as I am aware in Kicad.
From: noah
Oh yeah one more thing.
One more thing. The 7 volts coming from the regulator is right, That is a 7 volt regulator not a 5 volt regulator. Also the 5 volt regulator is right in case you can’t tell that’s a five volt regulator.Thank you.
Schematic
Noah,
KiCad is a fine schematic editor / layout tool.
You need 2 type of caps on the board. Large (bulk) to keep the voltage stable when something turns on and small to filter high frequency noise spikes. I would guess you would want at least 100uf on the +5 and multiple 0.1uf near each device. You probably want 10uf near the voltage regulators. I don’t agree with running 5 amp motors off a linear regulator. As a rule of thumb, the regulator should be at least three times the max load.
No way you are going to get 10 amps from the regulators or thru the L298P.
The schematic for the L298P does not show any protection diodes but the reference circuit does.
RESET is typically pulled up to +5 with a 10K resistor while the switch shorts to ground. If you want to use the Arduino bootloader you will also need a cap to DTR.
Just noticed that you have the USB port wired directly to the serial ports on the CPU. Not on a 328P. You need a USB to serial chip.
Thank you.
Dear: GG
Thank you so much for your help. I also failed to mention that the L298p is more than enough because my motors have a stall torque of 5 amps. They preferably need one amp. I will get to work right away and I’ll make sure to ask plenty of questions. Thank you so much 
From: Noah
Okay I have a few questions.
Dear: GG
What is a serial port chip and how do I use it? Do you have an example circuit for what I should be doing right with the reset switch? Since the reference circuit uses diodes I am having trouble getting what to do. Do I need to follow the circuit exactly for bidirectional control because they have so many example circuits I thought I was doing it right? I just added the capacitors to the regulators and thank you so much. Thanks!!!
From: Noah
Serial to USB
You can either add a serial to USB chip such as the FTDI or populate a 6-pin header and use an external device.
The diodes on the output of the L298 are for protection. Using PWM, we switch the power to the motor ON/OFF many times per second. The h-bridge can turn the voltage OFF but the current passing thru the motor winding wants to continue. The diodes provide a path for the energy to safely dissipate. Without them the current will try to find a path back thru the switch and will likely damage the device. Some h-bridges have diodes built in.
Thanks!!!
Thank you I’ll look into it.