MAX7219 Wiring Confustion

Rebuilding a scrolling sign project that I originally made from 74HC595's. Started a new circuit from scratch using MAX7219 chips. I was following this video on youtube as closely as I could https://www.youtube.com/watch?v=v1vRjOU_pGA&t=608s

I bought the MAX7219s. I cut my sign into 8 segment sections. I’ve wired up a breadboard test with 8x7(I only have 7 rows), and just the first 24 columns just to test out the idea.

I’m lost on something. I don’t understand how to wire the capacitors in the circuit correctly. I’m sure this is 101 for anyone into electronics, but I’m quickly over my head without a good foundation in electronics.

If I’m understanding it correctly, 5v is supplied to pin 18 of the max with a resistor between the pin and the 5v power supply.

Then pin 19....this is where I get lost. I am connecting 5v directly to pin 19, and in that same flow, adding one 10uf capacitor, and one .1uf capacitor. One leg of each on pin 19, then the other to ground. For the 10uf, I have the striped side with the ‘-‘ on the negative.

Does it sound like I’m doing this correctly?

Looks like the attachments didnt make the ride.

Two more images of my breadboard. no idea why, but I keep getting ngin x errors every time I try to post this.

From this picture of yours:

|500x273

1) The power supply (+5 volt) goes to pin 19 2) The 10uF capacitor goes from pin 19 to ground (and observe the polarity of the capacitor) 3) The 100nF capacitor goes from pin 19 to ground 4) The 40k resistor goes between +5Volt and pin 18

The 10uF and 100nF capacitors are in parallel and effectively go between +5volt and ground. However, they should be physically as close as possible to the Max's pin 19 ( its positive power supply input pin). Their purpose is smoothing (10uF) and decoupling (100nF)

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The 10uF and 100nF capacitors are in parallel and effectively go between +5volt and ground. However, they should be physically as close as possible to the Max's pin 19 ( its positive power supply input pin).

I would also add that:- 1) The ground they are connected to should be as physically close to pin 4 or pin 9 as you can get them. 2) I would prioritise the 100nF over the 10uF for getting physically close to the pins. You can normally solder the 100nF on the underside of the board across pin 19 and pin 4. 3) The 100nF HAS to be a ceramic type for it to be effective at all.

Other images: |500x254

|500x493

Clearly this in no way complies with 6V6's and Mike's specifications, but for one or two matrixes, this will no doubt work as an exercise. :grinning:

Unless you have a need for larger displays, the eBay modules are the most practical approach. |500x500 (Well, they were before Covid-19 when shipping fees were realistic! :astonished: )

Paul__B: . . . Unless you have a need for larger displays, the eBay modules are the most practical approach. . . . (Well, they were before Covid-19 when shipping fees were realistic! :astonished: )

. . . and delivery times . . .

Anyway, it always seemed ridiculous to me that a Chinese supplier would ship for free a single item of value 50 cents, when a local supplier here would charge a minimum of 20 times that for postage costs. It has now gone to the other extreme that if you buy 4 items at 50 cents each, you have to pay 4 times $3 delivery costs.

. . . and delivery times . . .

Well yes but, I ordered some rotary encoders last week and was given a delivery date of the last week in July and first week in August, they came in 7 days. I think it is dependent on the frequencies of flight between the two countries.

This is not the first time during the lock down that stuff ordered on two months delivery actually came within two weeks. For reference I am in the UK.

Anyway, it always seemed ridiculous to me that a Chinese supplier would ship for free a single item of value 50 cents, when a local supplier here would charge a minimum of 20 times that for postage costs.

This is because the Chinese government subsidise postage for exporters.

Grumpy_Mike: This is because the Chinese government subsidise postage for exporters.

Indicating the country actually wants trade! :roll_eyes:

6v6gt: From this picture of yours:

|500x273

1) The power supply (+5 volt) goes to pin 19 2) The 10uF capacitor goes from pin 19 to ground (and observe the polarity of the capacitor) 3) The 100nF capacitor goes from pin 19 to ground 4) The 40k resistor goes between +5Volt and pin 18

The 10uF and 100nF capacitors are in parallel and effectively go between +5volt and ground. However, they should be physically as close as possible to the Max's pin 19 ( its positive power supply input pin). Their purpose is smoothing (10uF) and decoupling (100nF)

Attachments in this forum must be less than 2MB or you get an error attempting to load them.

Awesome. Thank you and Grumpy Mike for the help!!

Paul__B: Clearly this in no way complies with 6V6's and Mike's specifications, but for one or two matrixes, this will no doubt work as an exercise. :grinning:

Unless you have a need for larger displays, the eBay modules are the most practical approach.

So i do have a larger and oddly shaped custom LED matrix made up of 44 columns and 7 rows that this is driving, so daisy chaining 6 together...You're thinking this method Im using isnt going to work? Any thought on what I can do to improve this so I can chain all 6 together?

Well my advice would be to stop using solderless bread board and start using strip board. You can solder things much more compact especially those 0.1 decoupling capacitors.

I notice from your photo that you have a long lead on the capacitor, that acts as an inductor and reduces the effectiveness of the capacitor at high frequencies.

With strip board you can even use surface mount capacitors soldered between two tracks. If the chip has the power on adjacent pins then they can be soldered between these pins.

Grumpy_Mike: I notice from your photo that you have a long lead on the capacitor, that acts as an inductor and reduces the effectiveness of the capacitor at high frequencies.

As mentioned in #5. :roll_eyes: