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Step up issues.

sc014a11d9.jpgxI recently bought a step up from spark-fun. The "DC-DC Boost converter NCP1400-5V". I power it with a 3.7v li po battery but it seems to be dead so I powered it with apporx 3.9v. I had used it in my micromouse and I am faced with a BIG problem. You see, I

connected( all in parallel)


  • 6 Pna4602m
  • 2 qrd1114's
  • 1 pic18f252
  • A 555 circuit which oscilitates 38khz for 6 ir leds
  • tb6612fng motor driver.
Currently, When i connect the basic stamp 2 with one of the PNA4602M IR sensors, I keep getting 0's and 1's when debugging. But when i hooked up the voltage from the basic stamp 2, the sensor could work perfectly well. This is also the case for the QRD1114 and i think it may affect my PIC.
Is this caused by unstable voltage or current? Is there a way to stabilize this? Thanks in advance!


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Difficult to guess but just need to tie grounds together. A picture (schematic) says 1,000 words.

Out of the parts you listed, which ones are drawing power from the Step-Up module, and which are taking power directly from the battery?

Some points to test:


  1. Measure the voltage at 5V out pin in the NCP1400 Breakout Board withou any circuitry;
  2. If the voltage is OK, sequentially, add parts of your circuitry. This tell you watt are happen with your Step-Up;

After win this issue, don't forget that 555 oscillator frequency changes with load. If you measure a 38kHz square wave at output oscillator, when you add the IR LEDs, this frequency will be changed to less then you want. Adjust it.

Pay attention on your Sensors. Measure the current throw the Emitters. Maybe, with 470R, the Emitter don't have enough IF (Forward Current) to operate properly. See:



Dont forget that for the circuit below, you need a Analog port on MCU, because you have a analog signal from sensors. 



The digital use for this sensor is:



Good Luck !

Thanks alot for the info forrequi. Crap! I have to de solder EVERYTHING on the top board. haha. I was able to use a 16f690 to control the motor drive at least. Thats a positive points. Will try my best to de solder stuff. I have a major exam in exactly 1 months time ! By the way, the 555 circuits that i tries to use wont work, can u suggest an alternative?
Invest in a bread board if you don't have one. It is always best to test out your circuits before you start soldering.
The circuit for "digital use" isnt it the same as the one I posted?  Do you have any idea why the PNA4602M is not working?



For digital use (with a digital I/O on MCU), the circuit is:


the circuit i propose for the qrd1114 cannot be used for digital? What do you mean by digital? 1's and 0's?


"the circuit i propose for the qrd1114 cannot be used for digital?"

R: Yes, they can be used for digital.

"What do you mean by digital? 1's and 0's?"

R: Mean that you don't need a A/D port to use this sensor configuration. Only you need is a commom digital I/O port. But don't spect read a sequence of "0" and "1". The digital use of this sensor is done by


  1. Setting the MCU I/O connected to sensor OUT line to HIGH;
  2. Wait at least 10us for the 10nF capacitor to charge completelly;
  3. Now, make the MCU I/O line an Input, a high impedance state;
  4. Last, measure the time for the capacitor to discharge by waiting for the MCU I/O to go LOW;


A Tip for item 4: Don't use a user defined variable (like a incremetal "counter") to measure that time. Use one of the 16bit Timers on your MCU (like Timer0). It's very easy, beliave me. But don't worry about how obtain a precision value and a wise conversion to seconds (or microseconds). Only you need is know if the discharging time occours with 3789 counters tics or with with 14521 tics of the Timer0. Fast discharging rate signifies a more reflective surface, like WHITE. A slow discharging sugest the oposite, a less reflective surface, like BLACK. So, if you only need know if your sensor are over a black or white surface, you don't need precision calculations over timer tics values. Seconds, Microseconds, etc, are only a convention, and only used to make citizens;


I'm really grateful for much help that you have given to me. I'm having problems with the 18f252 with asm. Take a look at my robot page for more details. THnkas!