Frequently Asked Questions (FAQ)
The board shows voltages on other A/D channels, even though nothing is connected.
This should not effect the readings of your current channel. Because of the internal multiplexing
done by the A/D, other channels will float. We recommend grounding all unused analog input
channels.
The board works but it doesn’t zero when grounded.
This is normal, you will get minor offset between all channels. These are very small and
consistent offsets that can be nulled out in software. Typically, all A/D routines incorporate a
calibrate procedure. By grounding all A/D channels and recording the offsets, they then add
these small offsets to the final value read.
Is it possible to build the board from scratch?
Yes, but we don’t recommend it, our several prototypes ended up being quite noisy, we were
only able to meet the specification of the Maxim chip after we professionally laid out the PCB
board. You might as well build an 8 bit A/D for you efforts.
How do I make differential readings?
You have 4 channels of differential inputs. You must place a .1uf capacitor between the negative
input and analog ground of each channel used for proper readings to be taken. The negative
input should not vary.
Negative Positive
Channel 0
pin 1
pin 2
Channel 1
pin 3
pin 4
Channel 2
pin 5
pin 6
Channel 4
pin 7
pin 8
The Mini Daq was working until I put a higher voltage than specified.
Try unplugging the Mini Daq from the PC parallel port and plugging it back in. This will reset
the board and release any latch up conditions. Damage to the Mini Daq may occur if you exceed
recommended input voltage.
Can the input to the parallel port be damaged?
You can damage the parallel port by not using proper TTL logic levels for the digital I/O. A
good practice is to provide a buffer such as a 74LS244 in your circuit. Check out our web page
for various interface circuits and projects.
How can I get more I/O?
You can run up to 4 Mini Daqs by providing 4 parallel ports for your PC. This will give you a
total of 32 A/D channels, 16 TTL input channels and 28 TTL output channels
How can I further protect my Computer from my experiments?
You can use a separate parallel port ISA card for the interface to the Mini Daq. If the maximum
input voltages have been exceeded, the separate parallel board provides an extra layer of
protection between your circuit and the motherboard of your PC. You can purchase 3
rd
party
add on ISA parallel port boards for $19 or less at your local computer supply store.
How are input and output ports connected to the PC?
The digital input and output ports are passed directly to your parallel port with no buffers or
protection circuitry. You must observe TTL levels or provide buffers to protect your parallel
