Qtr 8a doubt

hello ben,

i just got a qtr 8a sensors from pololu, altough the sensors are working fine …but the problem is that across 3.3volt bypass (to be specific 3.3bypass where you have indicated the users to short the bypass if we are supplying only 3.3v)
its getting heated up…only at that place
i want to know whether this is goin to damage the sensor array or is it okay…if it gets heated up…or is there some kind of defect …am using an arduino with 5v supply to the sensors…



I’m a bit confused by your description. Are you actually shorting across the 3.3V bypass pins on your sensor board?

- Ben

no i havent shorted the 3.3v bypass part am using a 5v supply from the arduino board,
you have told the user to short it only if we are going to supply 3.3 v.

but my question is its getting heated up at 3.3v bypass part,the place where we have to solder the headers and short it if we are supplying 3.3v, so am not shorting the 3.3v bypass because am not supplying 3.3v,
but its getting heated a bit at that part ,i have given the connections properly as indicated in qtr a manual which you have provided.
i have not touched the 3.3 bypass part for any circuitry connections at all ,

thanx for the reply,

It is normal for that area to get slightly warm: there is approximately 100 mA flowing through the two resistors just above the 3V3 bypass pads (each resistor is dissipating approximately 0.1 W).

However, if the area is getting hot (e.g. if it is uncomfortable to touch), I think you are potentially doing something wrong. Are you sure you are powering the sensor board from your Arduino’s regulated 5 V rail and not it’s VIN? Can you use a multimeter to verify that you are really supplying the board with 5 V?

- Ben

yes i checked using the multimeter and the supply is around 4.9v.
am using a shield for my arduino uno which has rows of 5v and gnd pins .
and am using these pins only for providing power supply to sensors.
am not directly giving from the VIN

thank you,

and i think getting warm is not a problem as ur stating its not a problem if its slightly warm,my doubt is cleared now
i would like to ask you a few more questions regarding my project .
am planning to make a line follower robot using following pololu products please tell me if i missed something important.

  1. baby orangutan b328 ,i am going to order this
  2. 50:1 HP micrometal gear motors,am going to order this
    3 qtr 8a sensor array, i already have this

these are my questions on baby orangutan 328p microcontroller board
1.) i have gone through the manual of baby orangutan controllers and i have i doubt on motor powering ,nowhere in the manual there is a mention on how motors get their power to run through baby orangutan b328 ,say if i supply 8v power through
VIN and GND terminals of the baby orangutan b328 is this enough input power to run motors, if i use 50:1 HP motors and 2700NIMH batteries
2.) if i use 50:1 hp micrometal gear motors from pololu how much voltage will reach the motors,ill be using 2 of these motors, for this project am planning to use 2700mah NIMH batteries since hp motors require a lot of current to stall.
3.)whether using HP micrometal motors on baby orangutan is suitable since its stall current is 1600mA if use 2 motors then current required to stall both motors is even high so will the circuits get damaged,i have minimal knowledge of electronic hazards so please bear with my simple questions in your perspective.
3.) can i directly plugin motors and sensors to the baby orangutan without making pcb to hold i know i have to make arrangements for power supply for sensors ie 5v and ground.
i will be using 6 qtr a sensors and 2 motors . i dont know how to make pcb design

thanks to the members of pololu for all the help.

Almost the full battery voltage is applied to each motor, so if you command the Baby Orangutan to drive both motors at full speed, both motors will have approximately VIN applied across their terminals. In general, the motors are supplied with a pulse-width-modulated (PWM) voltage. The height of the PWM is approximately VIN, and the duty cycle is controlled by the AVR on the Baby Orangutan. For example, if you want to drive a motor at 25% speed, the motor voltage will rapidly alternate between VIN and GND, spending 25% of each cycle at VIN and 75% of each cycle at GND.

By the way, 8 V is not a valid nominal battery voltage for NiMH cells. Do you mean 8.4 V (i.e. 7 cells)?

I suggest you use a battery pack with fewer cells, such as a 5-cell, 6 V pack. The Baby Orangutan is already a bit underpowered for those HP motors, and driving them at 8.4 V will make the problem worse (and it could negatively affect the lifetimes of your motors). As a general rule of thumb, you should avoid stalling motors for a prolonged period of time (this can damage the motors), but that becomes even more important in this case as the motor drivers on the Baby Orangutan will overheat if you use them to drive stalled HP motors for anything other than short durations.

You do not need to design your own PCB to connect your components. You can connect your motors and battery directly to the Baby Orangutan with wires. You can also connect your sensors directly to the Baby Orangutan with wires or through a breadboard or perfboard (I do not recommend connecting motors or other high-current devices through a breadboard).

- Ben