No Sensor Output

I think you're dealing with marginal voltage levels either at the 245's inputs or at its control pins /G and DIR. Since the thresholds and impedances can vary slightly for different manufacturers, some chips may work and others may not, even if all of them are OK. BTW, the suffixes N, P, etc. designate just the package and for your purpose have little or no influence.

Without further information, I'd suggest first checking that /G and DIR are at the proper levels (/G tied to ground, DIR to GND or VCC depending on the intended direction). Second, pulling the inputs up with 4K7 or 10K resistors tied to VCC (to conform TTL signals for your CMOS transceiver).

It would be helpful to know how your circuit actually is and what the PC is reading (I mean whether all zeroes or all ones).

Hello araees,

1. What is the voltage level of the conditioned signal recieved by the ADC?
2. What is the model of ADC you are using?
3. Is the ADC wired directly to the serial port of the PC?
4. Are the voltage levels between the ADC output and the PC serial port matched?
5. What kind of fluctuation is expected from the sensor?

Mike

ive further inspected the circuit and got following observations:

when the buffer ic is taken out of the circuit, the adc is sending 2mhz clk, sdofs with a pulse of 15khz and no data at SD0

when i connected the working 245 with it, sdofs pulse changed to a pulse of 375khz approx, there was noise at SDO(cause i was not using sensors and nor running my software for bulding pc comunication

but the ic that didnt work had the SDOFs pulse of about 60khz, no,data

SCLK signal in both(workig and non_working case) contains 8Mhz clock

and for the queries:

• ad73360 is being used.
• inputs to adc are signal s with mean value of 2.5v
• adc sends its data to DSPs then its sent to pc
• not getting your second last query
• im getting quants at my pc interface
  

Hi araees,

I'm not sure I understand, because your post is not clear. You replaced the 74hc245 and fixed the unit, so what is the problem? The IC tester may be running at a lower frequency, so does not simulate the situation.

"when i used the same chip with another system(actually the copy of previous one), that chip also behaved as the previous one and stili im receiving no output from the sensors."

This is not clear. Did a second chip of the same manufacturer fail to work in the original unit, or did the "bad" chip fail to work in a second unit? If it's the latter, then just throw the bad chip away.

regards

-S

There could be many problems, grounding included... As the previous poster noted, not enough information either.

One thing comes to mind and it's just a thought is that an IC with none or one with a suffix are usually very different IC's. So what came to mind is "Slew-Rate." If I remember correctly it's defined as the change in input voltage (from "0vdc" to "Logic 1" or Logic 1 to 0vdc) versus time... The general 74HC245/74HCT245 is listed at about 5nS... I can't remember how to do the calculation but that number is for the low to high transition, assuming the high to low is the same - I think the max is about 200khz... That other IC's slew rate maybe faster than that. Now looking over the specs of the AD73360... There's a bunch of information that's missing... Do you have the right values as noted by the 'design information' listed in the data sheet?

http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad73360/products/product.html

You've noted that there's noise in one of the outputs... The SDOFS output seems to be the indicator that serial data is coming out of the SDO line which can be sampled in respects to the sclk signal. But reading it again and here's a quote from the "General Description" on page 1:

"It features six 16-bit A/D conversion channels each of which provide 77 dB signal-to noise ratio over a dc to 4 kHz signal bandwidth."

Emphasizing "4 khz signal bandwidth."

Then there's 'load balancing' between the output(s) of the AD73360 and the inputs of the 74HC245(N/1p) to be considered, and what ever maybe in-between them... Another quote: "The SPORT transfer rate is programmable to allow interfacing to both fast and slow DSP engines." Also if this is a prototype at the present time, you might want to check the power supply for ripple/noise right at the IC's in question...

There are so many unknowns I'm just taking shots in the dark at the moment.