In order to try out the new I/O expansion bus for the MC3 I built a few quick I/O boards. The first one is a simple 8-bit DAC. I had an TLC7524 laying around. It's a simple DAC to interface to my bus since it has a built in latch. The analog side of this chip is however a bit confusing. After digging through the datasheet for quite some time and not really liking the example circuits I eventually focused my attention on the figure on page 5 - "voltage mode operation". This figure from the datasheet shows the resistor ladder at top and the digital switches beneath. In the application examples the REF pin is an input and the OUT1 and OUT2 are outputs feeding a differential amplifier but from this vague description I figured it might be possible to make it work the other way around with the REF pin acting as a single output. In that case OUT1 and OUT2 would be connected to Vcc and GND respectively to set the upper and lower limit of the DAC output. A much more simple design. Below is the schematic of my DAC board. The symbol is actually an AD7524 since it was the only one I had in the symbol library but the pin-out is the same as for the TLC7524. I added a voltage following op-amp as a buffer for the output and divided the output from the DAC. IMPORTANT: Check out Kevins version and comments below before building this yourself MK1 version - good for audio Update 2014-01-26 With the above circuit one could guess the output swing would be 0-2.5V with the 1:2 voltage divider but the divider and op-amp puts too much load on the DAC output and lowers the final output. Thank you Leo Bolier for pointing out this issue. The MK2 version buffers the output before the divider and improves the situation. MK2 version - higher output Update 2014-03-23 I ended up going with the MK1 version. It's just right for my needs. This is what the MK1 output looks like on a scope running a simple loop to generate a sawtooth. LOOP INCA STAA DAC BRA LOOP Note: Using the operation 'INC DAC' will not work here since the DAC value is not readable. As you can see the output voltage at $FF is only 1.3V. For my case this is perfectly adequate and the linearity is good. Update 2014-03-25 - Leo Bolier's version Leo kindly sent be his DAC design. This one is more elegant with an adjustable output and higher range. Thank you for sharing! This is how my (MK1) board ended up An RCA jack for output. A quite tidy backside. I was lucky that the arrangement of the DAC data pins matched my bus connector. The DAC boards occupies the whole 16 bytes address space of the I/O slot it uses but since I'm unlikely to place any other chips on this board I don't expect this to be an issue. Despite not taking any special actions to filter the supply or signal paths the noise level on the output is actually fairly low when used as an audio device connected to a line input. This could definitely be improved but I do not feel the need for it. Update 2014-06-23 A DAC can be quite useful as a debugging tool when connected to a scope. Writing debug values to the DAC and being able check for timing is one really nice feature to have. The problem can sometimes be to know when to actually trigger the scope for a stable display. Therefore I have added a separate TRIG output to my DAC board. The TRIG output generates a pulse when the DAC is being written to when A0=1 and omitted when A0=1. That way it is possible to select when a TRIG pulse is generated. MK3 version - trigger output Below is an example when the scope triggers on the TRIG signal and after that a series of 14 values are written to the DAC. Channel one is the DAC output and channel two is the TRIG output. Update 2015-10-02 - Kevin Baker's version Kevin kindly shared an elegant way of doing this. See his comments below. Thank you Kevin!