Part Selection for Circuit

[beb101]

Could anyone suggest a part/s to build the interface described in this Application Note (Figure 1),

http://pdfserv.maximintegrated.com/en/an/AN85.pdf

And also, what is a suitable resistor value?

Baxter

 

[SAborn]

Is there some reason why you picked this sensor as the DS18B20 would be a lot easier and well documented here.

 

[srnet]

Indeed, why do you want to interface it to a PICAXE system ?

 

[sedeap]

Is there some reason why you picked this sensor as the DS18B20 would be a lot easier and well documented here.

Indeed, why do you want to interface it to a PICAXE system ?

this looks like a similar issue to the question of why the man went to the moon?

 

[beb101]

No reason to use it with a Picaxe in a practical circuit. I just bought a Saleae Logic and a Bus Pirate and wanted to see what talking to a DS1620 with SPI looked like. The purpose of the question was to draw upon the repository of knowledge in the Forum relative to the interface. Thank you very much for answering a question with an inane question.

Baxter

 

[premelec]

You can bit bang the SPI signals as specified in the DS1620 data sheet in great detail [q.v.]. Try 4k7 for the resistor - should work ok.

 

[boriz]

Try https://support.maximintegrated.com/

 

[westaust55]

If you wished to specifically follow the diagram in the App Note then a resistor from 1 kOhm or slightly higher value should work.

The 74HC645 is an octal transceiver chip with tri-state (3-state) outputs incorporating a direction input and output enable pin that may allow you to omit some of the other logic gates (ie the AND and Inverter gates).

It should also be possible if using bit-bashing for the SPI comms to consider a direct connection between the PICAXE and DS1620 temp sensor.
For a M2 or X2 PICAXE part, using a bidirectional IO, when set as an input it is in effect a tri-state output in the high impedance state, so switching to input mode when not specifically sending data to the DS1680.
For a M or X1 part where separate input and outputs are required, the PICAXE input can be wired directly to the DS1620 data pin and use a 1N914, 1N4148 or similar signal diode between the PICAXE output and the DS1620 data pin. The didode Kathode (banded end) towards the PICAXE output. It may be possible to use a resistor of around 1 k Ohm in lieu of the diode.

 

[beb101]

westaust55 and premelec, Thank you for your pertinent answers ... The resistor value is what I needed. I am going to use this part/s for the logic,

http://www.ti.com/lit/ds/symlink/sn74lvc1g99.pdf

It seems to pack a pretty big punch for its size.

Baxter

 

[hippy]

It should also be possible if using bit-bashing for the SPI comms to consider a direct connection between the PICAXE and DS1620 temp sensor.

That's what I'd do. The SPI to DS1620 interface is only required for micros which only have SPI with separate DI and DO but the PICAXE can handle a direct connection. Adding anything extra will just complicate things unnecessarily.

 

[premelec]

Yep - what Hippy says - no need to complicate with external parts in this case...