DS1242

Help & Support Robot Parts
1

Hello

The DS1242 has 4 binary I/O ports.

Can some one explain how they are configured. They can’t be both inputs and outputs at the same time. I don’t see where each is setup to be either an input or an output port.

Thanks
Marty

2

Hi,

There’s no specific direction control. On both the dS1242 and the ds3484 the output is open collector with a pull-up resistor. With the output active the transistor is on and the output is low. With the transistor inactive (off) a resistor pulls it high. In this mode it can also be an input as an external device can pull the input low. So, If you want to use it as an input, just make sure the output is inactive (off).

Regards,

3

Thank you Brahim

4

Hi again
Both the dS1242 and the dS3484 digital I/O channels are rated at 100mA sink, while the driving transistor BC817 is rated at 500mA. (I need to drive a relay at 200mA)
Why soo conservative?
Any ideas?
TIA

6

Hi,

It is true that the datasheet of the BC817 transistor indicates that the collector current is rated at 500mA while the datasheet of the dS1242 specify that the outputs will sink current up to only 100mA. We have contacted the manufacturer and asked about this. We will post their reply here as soon as we receive it.

1 Like
7

We got Devantech reply and here is what they say about this

The 100mA limit is because the collector of the transistor is fed with 3.3v via a 2k2 resistor, this leads to around 1mA after volt drop. The BC817 has a gain of 100 in a worst case scenario, hence 100mA limit to be fully switched on.
If the customer wants 200mA he should be able to change the 2k2 feed resistor for a 1k with no negative impacts.