Hi. I am building a telescope focuser that I found on Source Forge. It uses an L293D motor shield on top of an Arduino Uno. All has gone well. I loaded a test program via the Arduino IDE that turns the stepper motor half a turn left and half a turn right. The motor works fine if I power the Arduino through the USB port, but not if I power it through the external power jack. The system must run independently of a computer. I can power the Arduino through a 5V cell phone adapter to the USB port and the motor turns normally. I am curious as to why the Arduino does not run the stepper motor when connected to the external power jack.
In all cases the light on the L293D board is on. The motor runs when 5V is applied to the USB port (with the cell phone adapter), but not if power is applied to the external power jack. I have tried 5V, 7.5V and 12V with the external jack.
I suspect that the Arduino is not passing signal to the L293D when the external jack is powered. Power must be flowing through the power pins on the Arduino, but not signal on the PWM pins. I also suspect that a jumper on the Arduino is involved, but despite a lengthy session on a lot of Arduino web pages I can't find anything about this.
Anybody have any hints for me? The project has been an excellent intro to the Arduino. It works very well. I look forward to focusing my telescope from my desk as opposed to standing outside in winter.
Stargeezer65:
I have tried 5V, 7.5V and 12V with the external jack.
The external jack on your Uno is connected to a 5 V voltage regulator. This voltage regulator has a voltage drop out, which means that if you provide a 5 V supply to the jack, your Uno will actually be getting less than 5 V. 7.5 V is a good choice for powering via the jack.
If you want to use a 5 V supply, you will need to connect it either to the USB jack or the 5V pin. Either of these bypass the voltage regulator and power the board directly. For this reason, you do need to be careful not to supply more than 5 V via the 5V pin/
Always use a separate power supply for motors and servos. Neither the USB port nor the 5V Arduino output can handle the current, and motors inject damaging electrical noise into the system that can reset or damage the Arduino.
The stepper is connected directly to the 5 motor pin jacks on the L293D motor shield that are designated for this purpose on the shield board. The L293D can run two steppers, 4 DC motors, and 4 servos. The shield draws power from the Uno and powers the stepper motor directly. There is facility to power the L293D board itself, and pull a power jumper to allow it to power the Arduino board below it. I haven't tried this yet. The USB plug on the Arduino powers the L293D and runs the motor successfully. The external power jack on 7.5V powers the L293D board but the motor does not run. I suspect that the Arduino is flowing power through to the motor shield, but not signal. Jumper setting on the Arduino?
Picture of the setup included. L293D motor shield is sitting atop the Arduino Nano. Stepper is connected directly to the pin blocks on the motor shield.
Sorry. This one should be clear. Not sure what you mean by "Fritzing" . Do you suggest I try powering the L293D motor shield board directly? Do you recommend 7.5V? The motor is rated 5-7.5V.
Please post the improved schematic, with clearly labeled motor, power and ground connections. Edit: What stepper motor are you actually using? The diagram says NEMA 17, which tells us nothing useful. Post a link to the exact motor you are using.
The stepper in the picture you posted is a unipolar stepper. It is NOT NEMA 17 size and is not intended to be driven by the L29X type of driver.
It is possible to do so with the pictured motor (if wired correctly), but you typically need a much higher voltage motor power supply due to the internal losses of the ancient, inefficient L29X design.
