Planning to build fetal(baby) heartbeat monitor for my pregnant wife

I am planning to build a fetal heartbeat monitor for my wife. Please suggest how to pick the heartbeat the fetus..??

Will a piezo do the job..?? and how do I convert the signal to audio..?

I doubt a piezo is going to be what you want. Fetal heartbeat is normally measured with doppler equipment like an ultrasound. You can often use something like a stethoscope and maybe amplify the sound from it, but then it gets really really really hard to tell the heartbeat of the fetus from all the other sounds going on in her body.

My advice is don't - you're unlikely to get it right, and either way, the outcome is not going to be popular.

As a father of four I reckon your Arduino device is far more likely to fail than is the baby’s heart, The Arduino will just cause unnecessary anxiety.

Babies are very sturdy things. Think of the conditions your ancestors lived in and survived in in the 13th century.

…R

Even if this is just for entertainment, all you are going to do is make life more stressful for the mother-to-be.

Groove: My advice is don't - you're unlikely to get it right, and either way, the outcome is not going to be popular.

Robin2: As a father of four I reckon your Arduino device is far more likely to fail than is the baby's heart, The Arduino will just cause unnecessary anxiety.

Babies are very sturdy things. Think of the conditions your ancestors lived in and survived in in the 13th century.

...R

Nick_Pyner: Even if this is just for entertainment, all you are going to do is make life more stressful for the mother-to-be.

You are all true. I appreciate your concern. I m in a dilemma too if I should do that or not. I am just too excited as a to be father.

But as an engineer I m little curious too that how does the fetal monitor pick up the heartbeat sound..?

Even there are iphone apps to detect the heartbeat through its mictophone. I dont know how accurate they are, and if a condenser mic can pick up such fainted sounds.

few examples of the monitors..

|500x500

|500x478

|385x500

The first picture gives a hint '3.0MHz'

You drive a piezo device with 3MHz, then mix that signal with the echoes - which will give a low frequency difference from 3MHz depending on the speed of things moving within it's range - like the baby's heart.

Allan

Those all look like Doppler devices from the look of the heads.

Inside of the probe there is one piezo for transmission (2 MHz, 3 MHz depending on the system) and one piezo for reception. The reception frequency depends on the velocity of the moving object or blood by the Doppler law. You subtract the two signals from each other. The frequency difference for moving blood seems to be in the range that can be heard so either they amplify it directly to the speaker or they somehow decrease the frequency and amplify. Here I am not sure.