If not mistaken i tried this before since this is a basic circuit...ermm....I retry again..mayb my brain hang at the moment...report to u guys few days later...^^ thanx

This post has been edited by knight: Dec 1 2006, 01:36 AM

still cannot larr..using that circuit..no finally trying on using an op-amp...hell, wonder y i can't amplify up the voltage..something is wrong here...

this is the circuit to amplify a 5v to 12v but wonder why it seems does not work...Anything wrong with my connections?? need assist here..

http://www.us.oup.com/us/pdf/microcircuits...ps/ua741-st.pdf

using a non-inverting amplifier..

This post has been edited by knight: Dec 6 2006, 03:01 PM


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What type of circuit u use?It would be useful for others to comment, if you got some circuit diagram that you are using.
Anyway, are u using 741 for voltage amplification? What configuration are u using?

using Non-inverting amplifier..is there any wrong with my circuit...duno what is this 'offset null' for..

Usually, when the difference of V+ and V- is zero, Vo should be zero(ideal). In some cases it is not zero, so you can use offset null (need to input some voltage in that pin) to make sure Vo is zero, when V+ minus V- is zero.

I dun think there is anything wrong with your circuit (just looked through), seem like inverting configuration. Most importantly, you need to get the data sheet of 741 and look for the minimum voltage need to be applied, to get the output. Try that.

What does this "amplify a 5v to 12v" has to do with the original light sensor? You are using a 5V PIC aren't you?

There is a flaw with my 22kOhm design because that makes input impedance seen by ADC become 22kOhm, while the maximum recommended is 10kOhm. However using 22kOhm won't cause it fail completely, it's just the acquisition time is lengthened. Nevertheless, changing 22kOhm to 10kOhm resistor also works.

If you're using opamp to improve the input impedance seen by ADC, the opamp should be powered by 5V and 0V, voltage follower circuit. But opamp is not necessary. Adding gain here is like nonsense to me.

Can you measure the output voltage of what I've shown? It should be more than 4V for one condition and less than 3V for another condition. Don't forget to power on the LED (IRED actually). And one more thing, did you burn the LED? (because many of my friend did this kind of mistake of not having correct resistor in series with LED; you must not connect LED to a voltage source without a resistor)

http://www.us.oup.com/us/pdf/microcircuits...ps/ua741-st.pdf

I posted the data sheet...

Yes, I just try 1st to see whether it works o not...then will try amplify the voltage..since the current are so small...erm...till now i still wonder y i can't get the input for the photosensor...

I dun think there's problem with this circuit as well..

This post has been edited by knight: Dec 6 2006, 05:48 PM


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^ Wrong circuit. Is up there, between resistor and collector, connect to PIC16F877. Measure the voltage, red probe on collector, black probe on ground.

neh...then means the PIC will always eat 5V even the phototransistor is on...the voltage drop at the resistor is 5v...

I tried that actually and it dun works..

I am not sure how much current is coming out of ur phototransistor ( you have to check the datasheet).
But what i can suggest is, u can maintain your configuration as shown in the diagram, but reduce the Rc value (resistor at collector) and put a new Re (resistor at emmiter) with higher value. In this way, voltage drop on Re wll go to your IC. Anyway, you can always use multimeter to check on the voltage level, when its bright and dark, and make a threshold value.

OMG...it's just the resistor problem only...the current input into the PIC is too low and even if it receive 5v but oso cannot work..Luckily I measure the internal resistance and get a bigger resistor for that..now it works...wahh..this getting me insaint...thanx guys...


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Suggest using a DC-DC buckboost is what you only need is voltage alone and not current to push the PIC to detect the signal, saves you power too

Don't need to use 5 transformers, just use a single one with multiple windings, you can't have 5 windings of course, but less work in one place always helps. Select power levels that are generally the same and then regulate from there. The 12 volt winding/line can be used to supply the 3.3v and 5v lines with high current LDOs (LM1117 or TI's UCC283), the 24v winding can be set to 15v with a trimpotted regulator based on the LM317 (pretty much a simple cap, a 20k trimpot across the control lines and a few resistors)

same like what I say before larrrr!

LM317 can also supply high current using bypass PNP Txistor. but at lower cost than high current LDO regulator.

omg...its been a while since this thread been updated..will work more on it ..guys...really sorry for the negligence

bump for u ... love building robots also

wow.. me too.. currently building h bridge..

ah.... electronics,
designed and build 2 robotic bugs for my FYP 2 yrs ago,
was fun, so much work for 3mths, result was great...
but had to part 1 of the bug wif my partner.... now left redundant in my house

may revive or build a v2 next !

This post has been edited by bcktang: Apr 2 2007, 11:44 PM