BS2p Demo Board Question

M Bush

I've been looking at the schematic for the BS2p Demo Board (Rev C dated 4/27/06) and I notice that the output of the LM2940 5V regulator supplies Vdd to the demo board, including pin 37 of the BS2p40 socket.· Now, if a BS2p is plugged into that socket, the onboard LT1121 regulator also provides Vdd to pin 37, according to the BS2p schematic.· Now my question is - doesn't that put the two 5V (Vdd) regulators in parallel with each other since their inputs are both Vin and their outputs are connected together?· What effect does this have on either one?

Thanks!

Mike

Mike Green

Good observation. Notice that the LT1121 will not have any input voltage since the Vin pin on the BS2p40 is not connected. Regulators like the LT1121 are designed for this type of use and should not be affected by being connected this way to a source of 5v (from the LM2940-5). The description of the power supply inputs for all Stamps (from the BS1 to the BS2px) indicate that either an unregulated voltage (for some > 6V, for others > 7.5V) can be connected to Vin or a regulated source of 5V can be connected to Vdd.

M Bush

Mike,

You mention that the Vin pin on the BS2p is not connected, however, the schematic I am looking at does show pin 40 (Vin) of the BS2p socket connected to Vdd - the same Vdd that is being driven by the LM2940!· I suspect this is a mistake and pin 40 is really disconnected so the BS2p is run from the external LM2940.· I don't have access to my BS2p Demo Board right now, so I can't verify.· I'll try to check it tonight.

M Bush

OK, I checked my BS2p 24/40 Demo Board and pin 40 of the BS2 socket (Vin) is NOT connected to anything. This is contrary to the schematic located here: http://www.parallax.com/dl/docs/prod/schem/BS2pDemoboardRevCschematic.pdf which shows pin 40 connected to Vin.

Mike