On 12/4/18 1:48 PM, Attila Kinali wrote:
On Tue, 4 Dec 2018 13:12:48 -0800
jimlux <[email protected]> wrote:
I maintain that it's the lack of a cheap RF front end that is the sticky
point.
Doing a 2-3 stage transistor based amplifier should give the signal
enough gain to be sampled with the ADC of a uC. I have such a design
sitting around, that I did a couple of years back for DCF77, but never
got around to actually built it (see attachment).
It is meant to be run from 4V, so that one can use an unstable/noisy
5V source with an 4V LDO and should give ~70dB of total gain. I used
BC547 in the simulation, but any NPN with decent h_fe and f_t should
do (eg 2N2222, 2N3904,...). The 2N5484 is a bit harder to replace,
as I selected it for its low V_th and narrow specified V_th range.
All that is needed for this to work is a tuned antenna, ie a ferrite
rod with a capcitor on it that is approximately tuned to 60/77.5kHz.
Attila Kinali
17 passive components and 4 active components. plus the loopstick and
tuning cap. I think you'd need pretty substantial volumes to get the
"assembled and delivered" price below $20.
I usually use the rule of thumb that the BOM cost has to be 1/5th to
1/10th the retail price. So $2.
You might get there.. the MMBF5484 is 12 cents in qty 100. I assume you
can find a NPN for less than 10 cents - The LDO might be the most
expensive part.
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