hi,
i'm trying to make one channel of the ADS1292 work as the analog input of a pulse oximeter. the photodiode is connected to a trans impedance amp and it's output to the positive input of the converter. negative is connected to ground.
everything works kind of fine but it seems that i got a timing problem. my led driving circuit is synchronized with the nDrdy output of the ADS1292 (fs = 1khz to take 1 sample each ms, the led driving signals are according to p6, http://www.ti.com/lit/an/sprab37a/sprab37a.pdf).
When receiving a nDrdy interrupt i reset the H-bridge and collect the ADC data via SPI. After 550us i switch on the led (R/IR alternating) and wait for the converter do finish (which is after 450us when nDrdy goes low again).
Is there a way i can better synchronize the sampling time of the analog signal by the ADC to the falling edges of the R/IR led drive signals? Right now i got good looking waveforms but when I don't switch on one of the lights (doesn't matter which one) i still receive a signal, which is a bit weird...
Thanks very much,
J