EMI impact of 74HC, 8051 and memory bus of a hobbyist project.

Hello,

does someone know how strong the electromagnetic emmissions of a homemade double-sided board (no ground plane) could be if there are some 74HC family, an 8051 cpu with quartzoszillator (6 MHz) and some sram and eeprom chips ?

The layout is not optimized, there is not an optimal return path for the bus signals. The power strips run parallel and there are decoupling capacitors.


I read that the 74HC family has EMI around 25 MHz decreasing to about 100 MHz because of its switching speed. In this region there could be some radio controlled toys in the neighbourhood and similar electronic devices.


Does someone know how strong this project could radiate ?

Hi,

it depends how the generated frequencies fit to the wire lentgh (to become a good sending antenna)
And it depends on how many signals are switched at a time.
PCB orientation...
and many other details.

Impossible to give an estimation.

Best is to go to an EMI measurement laboratory.

Klaus

According to the first paragraph of the question, the initial concern seems consistent with the title of the discussion, which is the EMI that a homemade circuit may be able to radiate in the surrounding area, but in the second paragraph, your remarks seem more focused on how the not-optimized layout can be immune to EMI. In other words, it is not clear whether you are concerned about the interference originated from your circuit, or about the sensitivity of your circuit to get interference from others.

In the book "EMC for Product Designers" by Tim Williams stood that the maximum allowed loop area formed by 74HC logic family should not exceed 45 cm2 at 4 MHz.

But is that the loop are of all connections from one package summed up or just per single trace ?