633 question

[R3nagad3]

I am about to purchase a 633, but still waiting on some better software to support and control the 633. Hopefully there will be some support for MBM5 and temp monitoring at the same time. But, my question is this: It says in the documentation on the web page that the 633 will support most Dallas Semiconductor 1-Wire devices. Will it support the DS2890 Digital Potentiometer? I would like to use it to control my 8 fans. Thanks
Ren

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[CF Mark]

Software is on the way.
EMail me and ill send you a beta copy of the current software.

Software can control 1wire ICs through the 633.

 

[CF Tech]

The 633 will act as an RS-232 to Dallas One Wire bridge. Software will be responsible for telling the 633 what transactions it is to execute on the Dallas One Wire bus. You can manually send transactions by using 633_WinTest (see Apendix A in the 633's data sheet for an ADC example).

I do not know of any software that will support an arbitrary Dallas One Wire device. Certainly possible though.

I do not think that most digital pots would be able to handle the current of a typical high-performance fan. Please be sure to check the voltage, current and power ratings of the digital pot before you proceed. You could use a digital pot or DAC in combination with some power device (FET, transistor, or perhaps a LM317 you are clever).

 

[jshamlet]

Linear pots not a great idea

You might consider using a digital POT in conjuction with a more traditional analog PWM controller (of which there are numerous examples on the web). In this case, the POT only has to handle a small current draw, as it will essentially be used as a voltage divider feeding a high impedance amplifier input.

The downside to PWM is that some fans don't react very well when the power is completely withdrawn and then applied, as is the case in traditional PWM. Symptoms involve stalling, whining, an inaccurate RPM readings.

If your fans are affected, you will need to add a low pass filter implemented either with coils or capacitors, for smoothing. With an appropriate filter, there should be enough current during the low transition to keep the fan motors from stalling at low speeds, and to maintain accurate RPM readings.

 

[R3nagad3]

Thats my issue getting accurate RPM readings. Also PWM will work for most of my fans, experimented a little to make sure. But, sometimes it causes my alarms to go off. Oh,well I'll figure out some way to get it to work. Maybe the PWM that I set up to test, is different than the 633's setup. Still trying to decide on buying a 633 right now. Thanks for all the help.
Ren

 

[CF Tech]

The CFA-633 will give accurate RPM readings for most fans even when the power is less than 100%. And yes, we modulate the power with PWM

Please note that it is up to you to make sure that your fan is compatible with the PWM control scheme used by the CFA-633. In our experience, most are compatible--but we cannot test every fan.

 

[Michael]

DS2890 with CFA633

Hi,

I've the same problem. I want do use the DS2890 with my CFA-633, but I've the problem to talk to. The commands I've used from the datasheet will not work - or I'm to not clever enough. Could anybody help me?

Michael

 

[CF Tech]

Did you try experimenting with the command format as shown in appendix A of the CFA-633 data sheet?

Things have to be exactly right with the DOW commands for them to work, but once you get it right, they do work

I used them on one of the Dallas SHA parts and once I got the commands exactly correct, they worked fine, so I feel confident in the firmware's bridge function.

 

[Michael]

Yes I did. The AD-converter DS2450 with your description in the appendix woks fine . But I can't read or write the wiper position with the DS2890. I've tryed in VB the following:

Public Sub DowRes(res%)
Dim Packet As PACKET_STRUCT
Initialize_CRC_Lookup_Table
'write the position
Packet.command = 20
Packet.data_length = 4
Packet.data(0) = 3 'deviceID
Packet.data(1) = 1
Packet.data(2) = 15
Packet.data(3) = res
Send_Packet Packet

'read the position
Packet.command = 20
Packet.data_length = 3 'deviceID
Packet.data(0) = 3
Packet.data(1) = 1
Packet.data(2) = 240
Send_Packet Packet
End Sub

Then the DS2890 answers, but nothing happens with the wiper...

 

[Michael]

Has anybody an idea???
Please!