Is there someone in this forum already used cellphone infrared from their project? got some problem here, Does it uses 40khz on transmit IR? and uses 40khz on receive? or it is plain Infrared beam, coz i read the data sheet it does not says there.

 

dhongskie, it's customary to start your own post if you have a question, not hijack someone else's. Most cell phones use IRDA which doesn't have a carrier, it's just straight up serial data sent directly to the xmitter. Look up the IRDA protocol. It starts out at a standard baud rate and then negotiates for higher ones. The protocol specs are available on the net.

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thnx all
first i use Vac/rect ,second i connt use AD7705 becuase we dont have it in gaza , but im really think that the problem is from the -regulator becuase when i put about -9v it output -6v and if i put less than -|7|v it output as -4 its not giving me -5v exactly

another thing is wrong that i put at the input and the output of the regulator 10u not 2.2u & 1u , another thing what is mean by "Low input offset voltage" to an opamp , and i search in the datasheet and i cannot find input but as i know it 330 as i put it between the IA .

thanx all very much
i hope to answer especially "Low input offset voltage"

 

hi,
i hope to answer especially "Low input offset voltage"

Most times when you build a opa circuit you will find that even with perfectly
balanced resistors and 0.00v input signal the opa output will not be 0.00v.

This can be due to the input offset error of the opa itself, during manufacture its not realistic to manufacture
the opa input stage to have 0.000v [zero] balance.

If you chose a good quality opa, this offset voltage will be very small.

However, if the opa output must be zero when the input 'signal' is zero, then its necessary to feed an external dc voltage into the summing junction of the opa that cancels the 'internal offset voltage', so you get zero out from the opa with a zero signal on the input.

Some opa's have two pins, to which you can connect an external variable resistor and 'adjust out' the offset.

Its important that the external dc voltage is stable.

Let me know if you understand.

EricG

 

thnx for answering
so can i say the source of the noise which i have is this small Volt level
and where is the summing junction, Is it pin on the OPAMP it self or i have to build summing amplifier

abbasi9999

 

hi eng,

The 'noise' in the system is not related to the 'internal offset voltage'.

The 'internal offset' is due to the opa's internal operation.

Other zero offset errors can be caused by component matching differences or errors due to the bridge voltage output not being zero without any load applied.
All the load cells I have used have this zero offset.

The 'zero errors' can be reduced by applying a voltage to a summing junction on an opa input.
I would suggest using U3A +inp as the summing junction.

From a stable voltage source connect a variable resistor to 0V, from the wiper of the variable connect a resistor to U3A+inp.

Chose the polarity of the stable voltage such that it will cancel out the zero offset. [offset could be +V or -V]

Noise sources can internally generated from your system or from external sources.

There are many potential sources of 'internal' noise.
Power supplies, poor decoupling, incorrect grounding, lack of screening, etc

As your load cells outputs are in the range of about 0mV thru 10/20mVolts,its important that you minimise the noise
before you amplify it and connect to the ADC.

I would recommend that you look at the www.analog.com site for applications data regarding 'noise'.

edit: application notes AN244 and AN106 as a starter.
What gain are you expecting from the amplifier in your drawing?

Is the 1K0 feedback resistor across the U3A a misprint ?.
If not check the CMR data, because the resistor from the +inp to ground ref is 10K0
EricG

This is only a brief/crude description of noise and offsets, read the reference material from analog and others for more details.