20 : 1 Transformer.

there are a few ESR projects for the Arduino on the internet already, have you found them for review yet, worth a look ie: http://forum.arduino.cc/index.php?topic=80357.0

I am not sure why you need a transformer (It would be a pulse transformer at that frequency btw). The testing I have played with in the past is to use the Arduino ADC directly and have a resistor divider to ensure any voltages are in the range of the ADC. but from my recollection, often ESR meters are also usable in circuit and therefor have to use voltages less that about 600mV in order to not turn on most diodes or other semiconductors

the idea being that you inject a pulse of known  current and measure the volt drop across the device under test while the pulse is being applied. As long as you do this quickly after the pulse is applied you will be able to deduce the effective resistance as the capacitance has not yet come into play by charging and therefor changing the virtually instantaneous voltage across its internal resistance

a perfect capacitor (If one ever existed) would have no voltage drop and therefor no series resistance. ( Couple this with the perfect power supply also with zero internal resistance and the draw would be infinite current and the world would come to an end as we know it lol)

there are a few ESR projects for the Arduino on the internet already, have you found them for review yet, worth a look ie: http://forum.arduino.cc/index.php?topic=80357.0

I am not sure why you need a transformer (It would be a pulse transformer at that frequency btw). The testing I have played with in the past is to use the Arduino ADC directly and have a resistor divider to ensure any voltages are in the range of the ADC. but from my recollection, often ESR meters are also usable in circuit and therefor have to use voltages less that about 600mV in order to not turn on most diodes or other semiconductors

the idea being that you inject a pulse of known  current and measure the volt drop across the device under test while the pulse is being applied. As long as you do this quickly after the pulse is applied you will be able to deduce the effective resistance as the capacitance has not yet come into play by charging and therefor changing the virtually instantaneous voltage across its internal resistance

a perfect capacitor (If one ever existed) would have no voltage drop and therefor no series resistance. ( Couple this with the perfect power supply also with zero internal resistance and the draw would be infinite current and the world would come to an end as we know it lol)

@Kiefer  Generally I agree with Peter but if you really need a transformer you can have fun and learn good stuff by winding your own.

If you decide to go that route ask again and explain the spec you need and I'll tell you how to do it.

MK