Digital Potentiometer Prototype

David researched and found a digital potentiometer by Intersil (X9511WP)-it arrived today. It’s a 10K ohm device with 32 up/down steps controlled by the three button array David salvaged from a printer (seen on the left). It works flawlessly with about 330 ohms per step. This device is limited to a wiper current of only 1ma. I also connected it to a 555 timer in an astable configuration. By replacing the two timing resistors with the digital pot, we can vary the ratio of the two resistors. The duty cycle is determined by this ratio giving good motor speed control via a mosfet. It works great and we think it is a better solution for control of the dive motor speed over a continuous mechanical potentiometer.

SOIC Carrier & Test Board

This is a closer view of the SOIC IC packaging, clamping test adapter (black) and prototype board.

Stepper Motor Control Circuit Prototype

We ordered a 3M prototype socket for the Allegro stepper motor controller 24 pin SOIC package and constructed a test board with wires for each pin. This assembly is seen in the lower left of the image. Parameters are set as: slow-decay mode (PFD high); full-step (MS1 &MS2 low); Rt=56K & Ct=680pf; Vref=4v; Rs=1.25ohm.

Validating the design, I measured V sense resistor=.32V and I motor supply=300ma which matches the design figures closely. Also, the square wave on both sides of the motor indicates the pwm is working. I tied the STEP input high with a pull up resistor. I have a 555 timer running at a very low frequency sucessfully driving the STEP input resulting in discrete rotation. Our objective is to use a stepper motor to control a claw on the ROV for grasping objects underwater. We are gathering a fine collection of stepper motors from old printers cast off at the local recycling station.

Note the black power supply (0-17vdc) at top that David built recently for our lab projects.

Mini ROV Design

David recently created this design for a mini-ROV. The concept is for a small ROV with a four to five inch diameter pressure vessel (sketch not to scale) that can be launched from a larger ROV. The diagram shows a complete mini-ROV using a single motor for propulsion and a parallel up/down-right/left rudder system with linkage controlled by stepper motors. The mini-ROV has a video camera in the front dome with lighting and blue LED’s. In the middle, circuitry can be seen for the stepper motor controller, motor speed controller, video-to-fiber converter and at the top a fiber controller with a cable back to the main ROV (including power).