I'm really confused about this transfer function
It's V_out = - (R_f/R_in) * V_in. You have it the other way round. It should be: -0.33 * V_in + 0.1375 * 12V.
As mentioned, it's good practice though not to rely on the power rails as a reference/offset voltage.
now I'm more confused Did I do the math wrong, or was @kassu 's transfer function wrong. Or is the circuit backwards? Im trying to learn but still on chapter one in the art of electronics
His/her calculation doesn't match the drawing. The circuit is correct, in that it's attenuating the input signal (gain = -33/100) and offsets it by 1.65v (= 33/240*12v), which is half the ADC range.
FWIW, you're looking at what's called an "inverting amplifier" or, more specifically, the "inverting summing amplifier" / "inverting mixer"; there's plenty of more or less non-technical information on the web for example.
Indeed, I had the numbers swapped around! Sorry, and thanks @gloom_and_glare for correcting. I updated the original post also to show the correct formula.
I was wondering what the difference between vdd, vdda and vddc. I am planning on using vdd for a reference voltage. If needing multiple reference voltages should I split them among the various vdd?
vdd is the digital 3.3V supply, use it to power external logic
vdda is the analog reference for the microcontroller adc and dac (gpio/in/analog and gpio/out/analog). It is 3.3V derived from vdd with a simple ferrite+bypass cap. If you connect potentiometers to gpio, vdda is the best reference.
vddc is the supply for the audio adc/dac. Also 3.3V, but it has a separate linear regulator from +5V.
FWIW/FYI: The purpose of VDDC is not evident from the currently available schematic (axoloti-core-sch-v10.pdf). There's just R15/NC, while U3 connects to VDDA.
Ah I see my mistake, the AVDD of U3 seems to be connected to VDDA in the schematic, but it really is connected to VDDC, not to VDDA.
First of all, could this thread maybe be pinned as a sticky at the top of the threads, because it's a very useful one.
Secondly, my question :
Can I make a hardware passive multiplier for the Gpio analog outputs (PA4 & PA5), by just wiring in parallel a few (how many?) outputs ?
My aim is to be able to control several gpio inputs using only one output. (on different boards)
Would it use up too much power or do something dangerous to the board ?
@mtyas ... pinning, I could but its a pretty long topic, with as many questions as answers.
perhaps if someone could pull out the salient information, we could have a topic that was easier to read?
... or is this unlikely to happen?
I was thinking about starting a new thread with some of the info I've gathered on this one... I must confess I am one of the main culprits of adding to the mess in this thread. Let me know if you all think that will be helpful and I can start working on it tonight.
To me there's a general usability issue with using Discourse for documentation. It's not apparent there is a User Manual section here and it's mixed up with discussions instead of a separate wiki. It does work, but needs to be called out or highlighted a bit more as it's hard for new users to find.
Hmm, I think its a consequence of me always using the "latest" tag at the top. If I go to home the User Manual is the first category in the list so perhaps not an issue after all. I do think however that a clean "Official Pin Guide" post is needed in the user manual.
Yes, I changed the default home page to be categories quite some time back... so when you first come here thats what you are going to see.
great suggestion, as I mentioned earlier, if someone creates it, I will move it, and also make it a wiki post (so other users can edit it) ... perhaps you could help @Illuminate with it.
It seems I can't post to or edit the new wiki post, so I will just post it here: I am not yet sure which type of input circuit I like best, but this one is possibly a bit better than the previous posted. This one only uses the supply voltage from Axoloti, so it is more general.
Notes:
- Again, the signal is inverted. So -5V to +5V maps to +3.3V to 0V.
- If no input is connected, it doesn't go exactly to the mid point, so the readout will not be "0". I couldn't find an elegant way to fix that, but if you use a minijack connector you can use the "normal" connection wired to ground (as shown), which is a reasonable solution.
- I haven't tested this exact circuit yet.
@kassu can you try now... Ive opened it up so "members" should now be able to edit the user guide topics.
thanks
( a test edit is fine, if thats all you have time for)
I've been watching this thread in hopes that someone has found a good voltage scaling application for Axoloti. I'm looking to scale Buchla CV (+/-15V) to the inputs, but haven't been able to find a good circuit. It doesn't look like the MCP600x series will accept that range of voltage - does anyone have a CV-in circuit they've had luck with?
Hi!
The circuit I posted just above can be modified for different voltages. It's either proper calculation or trial and error, I did the latter for you in a simulator. Set R3 = 10k and R2 = 300k to map -15V...+15V onto 3.3V...0V.
The MCP6001 can be used here, because the opamp never sees the full 15V swing of the input signal. It only sees much lower voltages due to the resistors scaling them down.
I've put jack inputs on most of my GPIO's, and I was wondering if I could have a multicord jack to patch one analog output into multiple analog inputs ?
Would it divide the voltages, or use too much power, or do something that shouldn't be done ?
If it is possible, couldn't I make a simple kind of dispatch-box, and maybe insert some kind of pot / variator on each output (so that I could dose the full PA4 range into all the different inputs) ? I don't know anything about electronics, so it's probably a silly question
